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Alternator System Troubleshooting
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Pelican Technical Article:

Alternator System Troubleshooting

James K. Thorusen

Dave Darling


3-4 hours







Applicable Models:

Porsche 914 (1970-76)

Parts Required:

New or rebuilt alternator

Performance Gain:

An electric alsystem that stays charged like it should

Complementary Modification:

Replace the battery
Editor's Note:  Refer to the current diagramin the 'electrical diagrams' section of this website to follow along with Jim's article.

    There are four connections to the alternator itself. D+, DF,D-, and B+. If you look at the Haynes book, what is not readily apparent, but is true nevertheless, is that the set of diodes that connect to the D+ terminal are a duplicate set (except for lower curent rating) to the ones for the B+ terminal, which is the actual high current output of the alternator. The D+ terminal is therefore a duplicate output terminal of the alternator, with less current capability. The lower set of diodes on current track 80 is common to both the D+ and B+ functions, and forms the ground return for both the B+ and D+ outputs. The DF or "Dynamo Field" terminal connects to the ungrounded end of the alternator field winding, and is an input to the alternator. The current supplied to the DF terminal determines the strength of the magnetic field that penetrates the output windings, and thus controls the alternator's output. The D- terminal is connected to the alternator frame, and is the ground return for the voltage regulator. The other end of the field winding is also connected to ground at this point.

     The Bosch alternator is incapable of self-excitation, or "boot-strapping" itself to an operating condition. Older DC generators and some U.S. alternators have residual magnetism retained in the core, or some other scheme to get enough field current to get themselves up and running. The Bosch alternator uses a different scheme. The charge warning lamp is connected between the ignition switch and the D+ terminal. When the car is first started, there is no output from the alternator at either the B+ or D+ terminals. The voltage regulator, sensing no output, is attempting to command maximum field current... it effectively shorts the D+ and DF terminals together. This places the D+ terminal close to ground potential, because the resistance of the field winding is not large. This means that there is +12 volts on one side of the charge warning lamp, and the other side of the lamp is grounded through the alternator field winding. Current thus flows through the lamp, lighting it. This same current, however, also flows through the alternator field winding, producing a magnetic field. This magnetic field is what the alternator needs to start up, and if everything is working correctly, that's exactly what happens. The alternator now begins to develop identical voltages at the D+ and B+ terminals. The D+ terminal is connected to one end of the charge warning lamp, while the other end of the lamp is connected to the battery via the ignition switch. Since the B+ terminal is hard-wired to the battery, and since both the D+ and B+ diodes are fed from the same set of windings in the alternator, no voltage difference can exist between these two points. The warning lamp goes out.

     The voltage regulator "watches" the voltage at the D+ point, which should be the same as that applied to the battery. It now changes the short between the D+ and DF terminals into a variable resistance. This effectively controls the field current (whose source is now the output from the D+ terminal, and not the charge warning lamp) and thus regulates the output voltage of the alternator.

     Fault conditions: When something happens to the charging system that causes it's output to be insufficient, the result is almost always a net voltage difference across the charge warning lamp, causing it to light. For example: Suppose an output (B+) diode opens. The efficiency of the main output is now considerably reduced. The voltage regulator does not know this, however, because it is looking at the D+ point. So, the B+ output is now lower than the D+ point and the warning lamp lights. Let's say that one of the D+ diodes failed: The D+ output is now reduced considerably. This means that the voltage regulator will have difficulty in maintaining sufficient field current for normal output. The field regulating resistance is low or short (between D+ and DF terminals) and the resulting load on the crippled D+ system drops it's voltage well below the battery voltage. Therefore, there is a net voltage difference across the charge warning lamp and it lights.

     The bottom line is that in order for your light to light, you must have a net imbalance in the outputs of the D+ and B+ sections of the alternator (or between the D+ output and the battery voltage, which amounts to the same thing).

     To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.

     To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad, with one other possibility:

     In the Bosch system, the size of the charge warning lamp bulb is critical. Too low a wattage bulb will not supply enough field current for "bootstrap" operation to be reliable. The Bosch book that I have states that the lamps must be at least 2 watts for 12 volt systems. If you have replaced your charge warning lamp recently, then too small a lamp may be your culprit.

I hope this is of some help.... Good Luck, Jim T.

Jim T.

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Comments and Suggestions:
Mohan Comments: My polo petrol engine car stoppped immediately and not starting. there is trip signal. while start with new battery again the indication is shown what is the problem, is it alternator
December 22, 2015
  Followup from the Pelican Staff: Could be. You will want to check charging system voltage and current to confirm the alternator is faulty. - Nick at Pelican Parts  
Mike Comments: OK, did some more testing. Just to reiterate, battery is new, alternator is a newly installed rebuilt Bosh from PP, regulator is new from PP. At idle D+/D- is 15.7V, and as engine revs, voltage climbs to near 20V and then cuts out. DF/D- is around 8V at idle, and as engine revs it goes to 10.5V and then cuts out. Battery is at about 13.2V at idle with no load, and as engine revs it goes beyond 16.5V. With all lights on, battery is at about 11.5V, and as engine revs it goes to about 12.5V and no higher. Was not able to measure current to battery. Thanks.
April 11, 2015
  Followup from the Pelican Staff: Current will be the indicator here, as voltage will increase slightly under load but current will increase greatly.

The voltage numbers on D+ are too high. It is over-charging. Either the alternator or regulator are faulty. - Nick at Pelican Parts
Mike Comments: Great article. My 914 has been exhibiting odd charging behavior since I've owned. it. Red light came on the other day, and so I replaced the alternator before I found this article. Afterwards, charging voltage at battery never came up above 12.5 volts, so I replaced the third party regulator with a Hella. Now charging at 13+ volts at the battery for first time ever, but red light is on dim at idle and gets brighter with engine speed. Voltage across D+/D- is 15.7 volts, DF/D- is about 8 volts. It seems that D+ is unregulated. Will this situation improve if I run it for a bit, or is something wrong? I sure would hate to have to do that alternator again. Thanks.
April 5, 2015
  Followup from the Pelican Staff: Could be a faulty alternator. What is current and voltage output, under load? - Nick at Pelican Parts  
nigel360 Comments: Warning lights for the air barks system dimming continously
February 15, 2015
  Followup from the Pelican Staff: Check the charging and starting system. - Nick at Pelican Parts  
nigel360 Comments: Alternator warning light goes while the enigine is running the battery is boiling
February 15, 2015
  Followup from the Pelican Staff: Could be a faulty battery or overcharging alternator. - Nick at Pelican Parts  
nigel360 Comments: This a truck no out from the alternator output lead to battery
February 15, 2015
  Followup from the Pelican Staff: Sounds like a faulty alternator to me. What is the vehicle? If voltage is low, then raises with RPM, the light will become brighter. - Nick at Pelican Parts  
Nigel 260 Comments: Alternator warning light becomes brighter with increase speed and goes out u know what could cause this problem pelican
February 15, 2015
  Followup from the Pelican Staff: Sounds like a faulty alternator to me. What is the vehicle? If voltage is low, then raises with RPM, the light will become brighter. - Nick at Pelican Parts  
Antoinette Comments: Hi Nick, I just placed a new regulator on the alt and have the following readings; 10 volts on the B+ and 14 volts on the D+ directly from the alt. DF still not connected. Battery is charged outside the car, and has 11 volts. Same reading with users on lights, heating ect.
Maybe I should try it with another model Bosch regulator, but with a spade connector for the DF wire?
January 19, 2015
  Followup from the Pelican Staff: You may have a bad battery cable. You have 10 volts at the alternator B+? COuld be a bad alternator. - Nick at Pelican Parts  
Antoinette Comments: http://www.audiforum.nl/forum/attachment.php?attachmentid=20203353
January 16, 2015
  Followup from the Pelican Staff: I can't view the attachment, as I am not a member of that forum. - Nick at Pelican Parts  
Antoinette Comments: Could I connect the DF to the D+ or the B+? Or maybe to ground? This alt has only two connections D+ & B+ and I have three cables?
January 16, 2015
  Followup from the Pelican Staff: I don't think so. Like I said, the wiring I have only shows your vehicle having D+. I would double check the engine code, part numbers and VIN to be sure they all match. - Nick at Pelican Parts  
Antoinette Comments: Yes Nick, the D+ and the B+ wires are connected. But the DF field wire is NOT connected, nor is there a connection on this alt to connect it to. It is hanging loose.
My question was; how can the alt give 14,3 volts and charge a battery when the DF is not connected?
I know it should be connected, but it's not. I've checked a few times and cannot find a spade connector for the lose DF wire. Still the alt was working for a while. Should I maybe change the regulator for a model with DF connection, as the model of regulator that is built on this alt has no connection on the regulator? If that is the case I still wonder how the alt was charging the battery for over 500km's without the DF connected!
January 16, 2015
  Followup from the Pelican Staff: I don't see that wire in the diagram, only D+. You may have a faulty alternator. - Nick at Pelican Parts  
Antoinette Comments: Sorry Nick, its a Audi A8 2000, V8 3,7 quattro tip-tronic.
How could the battery charge without a DF conected? When I picked it up from the garage it was charging 14,3. I checked a few times, but there is not connector for the DF wire on the alt. Now the alt isn't charging, I have 8 volts on the B+ but mainly cause I keep the battery charged so I can drive the car short distances.
January 16, 2015
  Followup from the Pelican Staff: The D+ wire should be connected and have power to the alternator when the key is in the run position. - Nick at Pelican Parts  
Chris Comments: Jim,
Thank you for this terrific information. I knew enough to short the DF and a 12v source, which did kick off my idiot light 74 VW bug but did not think about the D+ to DF test. The light did go very dim and then off again this way, which at this point I had hoped it would not so I would have identified the problem at least.
The interesting part is that after running this test, I removed the jumper wire from D+ and DF and restarted the car, fully expecting to see the light on again. Now however the light is operating properly! Could I have somehow reenergized something from this car having sat for the past 5 years? I would hate to think it is fixed only to find out that it was a false hope.
January 16, 2015
  Followup from the Pelican Staff: Could have jump started the regulator, I haven't seen that before, but you never know. I would replace it just in case. You don;t want to get stranded. - Nick at Pelican Parts  
Antoinette Comments: Hi, very interesting site, I have a problem with my alternator. I had it replaced recently nad the garage placed a used alternator. The car was running good for about 500km, charging 14,3 volts. Now it stopped charging. When I looked under the car I saw a loose wire, a green one and my best thoughts are it is the DF wire. I can not connect this wire to any point. Could it be the garage fitted a wrong model alternator, without a DF connection? I found out this model Bosch can be fitted with two different types of regulators; one with and one without spade connector. Could this be my missing connector for the DF wire? How could the battery be charged for 500km's without the DF connected? I was driving with lights, heating, screenwipers, radio and so on for 500km's so I don't think I was simply using up the battery, it must have been charging for a while without DF wire connected. Is there a other way to connect the DF somewhere to the alternator, like to the D+ or the B+? Thanks for any help!
January 16, 2015
  Followup from the Pelican Staff: You didn't mention what vehicle you are working on. A field wire should be attached. I would return to the garage and ask them to repair the alternator. - Nick at Pelican Parts  
Dale Comments: Is a bad battery capable of taking a 100% charge?
January 11, 2015
  Followup from the Pelican Staff: A battery is capable of being 100% charged, 12.6 volts. - Nick at Pelican Parts  
Discs even Comments: Nick, yesterday,at speed,gen light came on and stayed on. Am planning to do tests as suggested but have to admit to being electric idiot. Can you explain in further depth the set up for the tests suggested. Am speaking of paragraphs beginning at "to troubleshoot the problem"... That paragraph and the next. For a genius that may make sense. To a noob like myself... More detail is needed. Thanks. Karl
September 9, 2014
  Followup from the Pelican Staff: You'll need a wiring diagram. You can load test the system as described below. If it is not charging, you then have to confirm the voltage regulator and alternator have power and ground, if they do, excite the regulator, the alter should become magnetic (with the engine off), a wrench will stick to it.

here is an excerpt from a tech article:

Always check the voltage of your charging system under load, voltage should be within 13.2: 14.5 volts d/c. To load, have engine running at idle, turn on headlights and HVAC blower motor. Never disconnect a battery cable while engine is running to test alternator, you may cause damage to alternator or other electrical components from the surge in amperage. Before performing any tests of your alternator, charge and test your battery. If the battery is faulty, your alternator tests will not be accurate. - Nick at Pelican Parts
DJ Comments: Follow up. I was looking at the wire diagrams and it appears that the 'exciter' wire should have battery voltage when in run and start. It does not have voltage 1 Volt. I'm guessing that there is a short to ground somewhere or an open circuit. Where does the exciter wire attach upstream of the alternator? Thanks, DJ
August 29, 2014
  Followup from the Pelican Staff: Likely to the bulb. If you add fused power, does it charge?

I am going by your info, as I don't have the wiring in front of me. - Nick at Pelican Parts
DJ Comments: 1998 328i convertible. Never getting more than 12.5 volts directly from 'red' alternator output. 'battery' light always on. Battery not charging. Battery new and takes charge fine. If I measure voltage from second wirethought it was black but I guess it could be blue, how much should I be getting? How exactly do I test it?

August 29, 2014
  Followup from the Pelican Staff: I answered you under your other question. - Nick at Pelican Parts  
Regi Comments: 318ci E46
have fitted new alternator after previous failed on the road. Ignition light continuous on full not dimmingwhen engine running - battery newish and good - 14v over battery when engine running so charge ok - looks like about 10v on the blue wire from the alternator - suspected this so got 2nd exchange alternator - senerio still the same! help appreciated.
August 19, 2014
  Followup from the Pelican Staff: The blue wire should have charging system volts when the engine is running. There may be a short int hat wire or circuit. - Nick at Pelican Parts  
curleyman Comments: after start ... red gen light stays on, eventually may go out.75 914-4.most evident after repl starter installed, HELP. Battery died after last time, needed hot shot.
August 10, 2014
  Followup from the Pelican Staff: I would double check the ground and positive connections to the starter and battery. Perform a voltage drop test. There may be a poor connection. - Nick at Pelican Parts  
Buddr Comments: I have a bmw 318 I, car was a no start, so car running checked the battery and it had 12.56 volts, sounds like battery voltage to me so I replaced the alternator, same problem. 12.56 volts ??
July 3, 2014
  Followup from the Pelican Staff: Is there power at the main power lug on the alternator? Could be a bad wire or open circuit. Have you tested the battery? - Nick at Pelican Parts  
Warren Comments: Follow up:
I just had to clean the contacts of the fuses under the dash, every thing works fine now
May 7, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it. - Nick at Pelican Parts  
lisa Comments: My v reg BMW 323i is havng battery issues on drive when not in use the battery is dyibg...i bought a brand new one and it died again..i have been told to disconnect a thhinner black wire that goes into the battery by someone who tells me its a common fault and it will stop the problem. When the battery problems started my partner removed something from fusebox thinking it would help but now i cant see how fast im going or mileage or battery lights or pi ture on dash of car that tells me if lights gone or doors open.......please help
May 1, 2014
  Followup from the Pelican Staff: You may have a parasitic draw. You'll want to monitor the draw on the battery when the vehicle is asleep. Here is a list of the specifications: http://autotechdiagnostics.com /?p=185
Once you confirm there is a draw. You will have to isolate the circuit with the draw. Then determine which components on that circuit is causing the draw You can isolate by removing fuses. be sure to have all the latches on the doors and hood closed (pin switches) so the vehicle will sleep during testing. If it wakes up, you will have to wait until it goes to sleep again. - Nick at Pelican Parts
Warren Comments: Hey there, big fan of this company, ordered many great parts for an old e30 here. Now I have a 914. The generator light does NOT come on with key on engine off. Engine starts and runs fine all day, charging voltage of 13.4 at idle with no loads, battery has never died. When turn signals or hazards are activated the generator light comes on dim and the flasher relay buzzes but no indicators on dash or at external light. I don't know where to start diagnosing this one, hope you can help!! Thanks for reading.
April 25, 2014
  Followup from the Pelican Staff: Start by checking charging system voltage under a load. If it is still OK, you may have a voltage drop problem. Voltage drop test your grounds. - Nick at Pelican Parts  
tomasin944 Comments: hi! I have a 1989 944 turbo, with original alternator. At around 4500 rpm the exterior lights and dash voltmeter gauge start to fluctuate wildly to a point where im blowing headlight fuses. Up to 4500 rpm everything is fine. can you help me what to check or replace?
March 28, 2014
  Followup from the Pelican Staff: I would check the charging system under a load. The regulator may be failing, over-charging the system. - Nick at Pelican Parts  
ah chin Comments: could you let me know why,when stop engie for 5min,reads about 12.72v,and after 4hr reads 12.56v,and it keep on dropping by.1v everyday it this normal regulator
February 14, 2014
  Followup from the Pelican Staff: Battery voltage will drop as the vehicle sits, it will normally discharge. As long as voltage doesn't drop below 12.2, your battery is OK. - Nick at Pelican Parts  
Aaron Comments: Thanks for the reply a year later lol. I found the issue, fixed it and soon after pulled the chute on that car. The issue was the battery...
November 24, 2013
  Followup from the Pelican Staff: Thanks for the feedback. We are trying to get through all of our tech questions so we can provide more timely service in the future. Thanks for using Pelican Parts - Kerry at Pelican Parts  
Garpue Comments: Thanks for your corporation
Meshach G. Robert
October 14, 2013
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
overrev Comments: Do anyone here have a pdf of bmw m20b20 Bosch Alternator wiring diagram?. Need help here. Don't know where to connect the wire's just after replacing new alternator. I didn't memorize which goes where before replacing it
August 10, 2013
  Followup from the Pelican Staff: You posted a BMW question in the Porsche forum. By the way we do have repair manuals for sale that contain the wiring diagrams you need. They are also helpful for many other projects and repairs- Kerry at Pelican Parts  
mooshimooshi Comments: MY PROBLEM IS BIG......I have a 74 Porsche 914 that has sat for 13 yrs....I attemped to work on after its first owner spent thousands at a local shop with no results.....I replace most of the ingnition componets and it started after dialing in the timing...It ran for 13 minutes when an large spark came from underneath...and the system went dead....I have no power what so ever....come to find out the wire going to the started touched the exhaust and melted then shorted.....I am lost as to what to do first...can you help....
July 6, 2013
  Followup from the Pelican Staff: Try a new battery and a new cable, after that you may need a fuse box and ignition switch but I'm just guessing If your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume and quality. Once you figure out what is missing, it will be easier to diagnose.

- Nick at Pelican Parts
Ian Comments: I have a 1991 318i. The alternator does not charge until i rev the engine to 3500 rpm. Before starting the battery reads 12.4 volts, after starting it reads 11.6 volts until i rev to 3500 rpm, then the volts at the battery goes up to 13.6 and stays charging at that even though the rpm is reduced. When i shut off and start back, its the same thing. I need to rev to 3500 rpm to get to 13.6 volts. what is the problem with my car?
May 31, 2013
  Followup from the Pelican Staff: Sounds like a faulty alternator to me. - Nick at Pelican Parts  
john Comments: need help with my 1994 318i it starts up fine but if i remove one of the battery terminal car dies.

checked the following:
battery good
alternator is good
ground connected
even switched up alternator and battery with my friends same exact car and still the same.
battery light indicator remain on and drains battery

thanks in advance
May 16, 2013
  Followup from the Pelican Staff: First, do not remove a battery cable when the engine is running. It can create a voltage spike that will damage control modules.

If the vehicle isn't charging, there is an issue with the alternator. The small blue wire at the back of the alternator goes to the instrument cluster. If you use an incandescent test light and attach one end to battery positive and the other to the blue wire, the alternator should charge. If it doesn't, the alternator is faulty. - Nick at Pelican Parts
Cundiah Comments: Hi, Ignition light goes out when engine running but no output from alternator, any idea on the most likely cause? Thanks in advance.
March 20, 2013
  Followup from the Pelican Staff: This could be a faulty regulator or alternator. Try to full field the alternator, if it charges, replace the regulator. - Nick at Pelican Parts  
Aaron Comments: Hi Wayne. I have a 1994 325is the car is eating alternators. The only thing I have noticed is the excite wire when disconnected and key on shows 10.6v batt is full charge. When I connect the excite wire to the alt and turn key on it only shows 1.6v. Any thoughts
December 23, 2012
  Followup from the Pelican Staff: 10.6 volts is low and may cause the alternator to overcharge. If the sense wire shows low voltage the voltage regulator will try to raise voltage because it thinks the car has a big electrical load. I am going to need to know what the voltage on the sense wire is with a good alternator and what is the output voltage from the large stud. It would also help to know what the amperage output is at idle. - Kerry at Pelican Parts  
Bkoz Comments: I sure wish I would have found this article sooner It would have lead me right to the problem. 1988 Mercedes 260e alternator not charging. replaced alternator and found that I had a bulb of the wrong wattage installed. I would pull the wires off of D+ and I had voltage there but would not charge. AutoZone tested the alternator again still passed.I swapped lamps in inst panel because the resistance was higher on one. Bingo that was it. Yes I would not have learned as much but was my old alternator really bad. Who knows because it was bearly charging 12.5 volts.
August 9, 2012
  Followup from the Pelican Staff: Thanks for the Info. We appreciate it. - Nick at Pelican Parts  
armsup Comments: The guys that painted my 1969 RSR clone pulled the wires going to my external voltage regulator and I'm not sure how they were connected. I've got an orange wire, brown/white stripe and double blue wire. Can you tell me which of these goes to the D-, D+ and DF connectors on the regulator?
May 25, 2012
  Followup from the Pelican Staff: Should be close to this:

Red - terminal 30
Blue - D+
Brown - D- - Nick at Pelican Parts
haasman Comments: I appreciate this section on alternators. Great info.

I am wondering if anyone has any suggestions for me- I have a '70 914-6 that when the headlights are on, they slightly dim and then brighten in about a 1-2 second cadence when driving along the road. I should have check to see if they do that at idle before writing you. Does this sound like a bad regulator in the alternator?

My other electrical concern seems simple but has be-fuddled me. When using the turn-signals both indicators blink when signaling either left or right. I had been told that possibly it was the strn signal housing grounds but they checked out. I was also told that in the dash, where the lights are mounted need to be grounded but I never have seen a ground in a wiring diagram for that.

Before I started a simple "parts replacement" I thought you might have some suggestions.

Thank you in advance-
April 30, 2012
  Followup from the Pelican Staff: This sounds like a faulty alternator. It wouldn't hurt to check the grounds to the headlights. But in the end I think you'll find your alternator ins't charging. - Nick at Pelican Parts  
AussieShane Comments: Have a 97 Toyota Hilux 2wd 2.4lt ute. Mechanic Recently replaced Alternator with new one. Unfortunately the previous alternator was drowned in oil from a leaking timing chain seal bearing which soaked the engine bay in oil. Was told the oil burned the old alternator out and blew the 80amp alternator fuse. Replaced alternator and 80 amp fuse. Am told alternator is charging as required BUT the warning lights on the dash battery/brakes still remain on. the lights arent as bright and are lit to half bright. What could be the problem???
November 28, 2011
  Followup from the Pelican Staff: This site deals with European car issues primarily. Sorry. - Nick at Pelican Parts  
al Comments: 2000 chevy blazer. new alternator, battery good 2 yerars old won,t take charge. com
November 20, 2011
  Followup from the Pelican Staff: Even if it's maintenance free try prying off the covers used to fill the battery to check the electrolyte level. Maybe from overcharging electrolyte has leaked out of the vent. - Kerry at Pelican Parts  
Lou Comments: Wayne, do you supply the bearing for alternator for 2000 323i.I believe the E46 & E36 323i and 328i use the same alternator and is it that difficult to disassemble and reassemble? It makes a clacking noise, like bad lifters or valves needing adjustment. I checked both, the sound appears to most definitely coming from the alternator.
October 11, 2011
  Followup from the Pelican Staff: Conatact our parts specialist at 888 280 7799 but I believe you are going to have to buy the whole alternator - Kerry at Pelican Parts  
txtwin Comments: I have an 89 911 and while driving the stereo amp will cut in and out. At night, this happens to correspond with all the lights on the car dash and running lights dimming at the same time. Cruising on the freeway, this doesn't happen, but does resume once I am in stop and go traffic. The battery is brand new, and while idling the alternator is charging to 13.4v. If the car isn't driven frequently, the battery will drain within 2 weeks of sitting. Is it a bad alternator, or a bad voltage regulator? If not, any ideas?
September 15, 2011
  Followup from the Pelican Staff: I would check the alternator charging voltage with all the loads on. Turn on your blower, headlights and radio, is voltage still good? If not, replace the alternator. - Nick at Pelican Parts  
Bill Comments: If an alternator "passes the Auto-Zone bench test, does that imply that all of the diodes are properly functioning?
September 9, 2011
  Followup from the Pelican Staff: Probably. Conventional bench testers look for ripple which is the phases of electrical current making it past the diodes. - Kerry at Pelican Parts  
eztuner12 Comments: How do I know the proper Voltage regulator for my Valeo Alternator. My car VIN # AS71156
Part # please
September 1, 2011
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
eztuner12 Comments: Hi Wayne
First, I have been extremely pleased with my purchases at Pelican and the services provided by you team force, keep up the good job!
Today on my way to replace the oil filter housing gasket & o-rings I first had to remove the Alternator but at the time I was unbolting the Alternator rear side bolts in order to remove the 2 wires, thick red wire & thin blue wire, the base screw where the blue wire is bolted broke off from the inside area platform of the alternator, certainly the bolt was extremely tight, but the bolt that holds in place the red wire as very easy to unbolt, This Alternates has never been removed since the car was new. I sent a message to your tech support in order to find out if the rear section under the black plastic covers where the wires screws are attach to the Alternator can be replaced and if it can be done to forward me the part number.
On the other hand if the case is that I have to swap for a new Alternator, “which I hope not” I am planning to go for a “Bosch High Output Alternator”, since I read on the Bosch site that it can deliver amperage output up to 200 amps, while also providing maximum available amperage at ”low engine RPM”.
I think this would be a solution to my issue that when my car is at low RPMs @ 800 the head lights & interior lights including the control panels Cluster dims when the A /C compressor, rear defrost or electric radiator fan turns on, even the A/C won’t cool well at this point. My only concern about this Bosch High Output Alternator is if it would be proper for my Bimmer, I mean it won’t affect or damage any other electronic equipment from the car?
My car as you might know by now, is a 1997 BMW e36 318is/M44 German Version, automatic transmission with a Downing Atlanta Supercharger I installed a few years back. The car has @ 34,000 original Kilometers @ 21,250 miles. VIN # AS71156
I would value and appreciate form you any suggestion regarding my issue & dilemma about the Alternator
Certainly looking on for your reply and help…
Have a great day!
PS A pic of an Alternator with the 2 fix screws were the wires are to be hold bolt. The one that broke from its base is the lower small one.
July 21, 2011
  Followup from the Pelican Staff: If your vehicle has the alternator shown, you will have to replace it. i am not aware of any repair for the studs. - Nick at Pelican Parts  
Armand Comments: I have a 77 Peugeot 504 gas with a Bosch 50 amp alternator
I have a new external voltage regulator with post EX, +
I don't know how to hook up the wires from the alternator
The alternator has 3 post D+. DF, D-
Which wire goes to where?
June 7, 2011
  Followup from the Pelican Staff: I don't have wiring for your vehicle. Check if this matches your vehicle:

Red - terminal 30
Blue - D+
Brown - D - Nick at Pelican Parts
BT Comments: I have a component car that is using a 914-4 engine with carbs, and we have basically scrapped the wiring from the donor 914. We are still using a stock 914-4 alternator and external regulator, but I am stumped about how to wire the aftermarket generic car wiring harness to make the charging system work. I have a circuit on the new harness that is marked "Alternator excitor" and it gets 12V when the ignition is on. I was told by the harness maker that I am supposed to tie this wire in to the DF terminal, so I spliced it into the green wire between the regulator and the alternator. I have not installed any alternator warning light, and I think that is the problem. The questions are:

Does the alt excitor power go to the DF or the D+?
If I need an alt warning light, where does it go in line to the D+ I would guess.

My guess is that the alt. excitor is supposed to power a warning light and go to the red wire between the regulator and alternator the D+ wire.

We got some smoke from the external regulator with our current setup when we ran the engine, so I am pretty sure I need a new regulator, I am just hoping to get it right the second time!
June 1, 2011
  Followup from the Pelican Staff: You'll need the circuit with the bulb to go to D+. That should be ignition feed B+ through the bulb to D+. - Nick at Pelican Parts  
watiffated Comments: Hi, I need your help to troubleshoot my alternator. The light did light up, I change an new alternator new regulator new battery, connection is fully right after many round check. At certain time it charge but at certain time it don't. I using a 24v vehicle. So what will the best way to troubleshoot it ?
April 19, 2011
  Followup from the Pelican Staff: You didn't mention what vehicle you have.

Perform a charging system test, load the alternator and confirm it can maintain a good output. If it cannot, voltage drop test the power and grounds. If everything tests good, the alternator is faulty. - Nick at Pelican Parts
cathy Comments: battery new alternator rebuilt new regulator . i will run 914 4 1970 all day . once i put on light radio it will not charge car will die . then i have to keep two battery one for back up and this stink ,tranny ground good firewall ground good . someone sad there is a way of turning up volts on alternator or regulator how ? and charging light on dash red light ? help
April 13, 2011
  Followup from the Pelican Staff: Sounds like it's only trickle charging and not fully charging your battery. This is indeed most commonly caused by a bad or poor ground between the engine and the chassis. I would check the resistance, and/or try adding another ground strap. There's no way to "turn up" the amps on the alternator unfortunately. - Wayne at Pelican Parts  
dhorrnet Comments: Battery dies, so i replaced it. The same day the new battery dies. So is that telling it's my alternator?
March 23, 2011
  Followup from the Pelican Staff: Yes, that is a good assumption - the alternator is not properly charging the battery. Make sure all the ground straps are properly attached on the engine. - Wayne at Pelican Parts  
Fireman Comments: Hi great read and very useful. I have a VW transporter that gives battery voltage to the D+ wire until you connect it then its 1.6v regardless of engine running or not. Light stays on and no charge. Make up a wire direct from battery + with an inline bulb and this extinguishes when the engine starts and new alternator charges fine?
February 3, 2011
  Followup from the Pelican Staff: I'm not a super alternator expert, but I believe that you will see this behavior when the diodes in the alternator fail. The light will sometimes stay on all the time, and you may even run your battery down from the light being on all the time. The solution is to replace the three or so diodes in your alternator - I think that will fix your issue. - Wayne at Pelican Parts  
JCoop Comments: My 84 targa rpm gauge fluctuates wildly-and now has seemed to settle down but is about 400 below normal operating range during idle and shifting sequence. Some suggest it is the alternator, some the voltage regulator. Any help you can provide would be helpful. Thanks
January 13, 2011
  Followup from the Pelican Staff: These tachs can be sensitive, I've seen this behavior when the tach is getting old and needs repair. In general, the alternator or regulator should not affect the proper operation of the tach. - Wayne at Pelican Parts  
pickleboats Comments: Hi
2001 E46 new alternator new battery.Car has no alarm system. No alternator output and No battery light when you turn on ignition and run . Any sugestions? There is also 12 volts at each of the terminals on the small connector connected to the alternator.Bothe the 5 am and 7.5 amp fuse are good. HelP!!!!
December 8, 2010
  Followup from the Pelican Staff: Hmm, maybe the internal fusable link for the battery got blown somehow. There is an internal fuse somewhere in the system that protects the car if there is a major short. - Wayne at Pelican Parts  
CL Comments: Hello, I have a 1989 E30 320i with the M20B20 six. The car has refused to start completely, after failing to start a couple of days ago. In the first instance, it cranked after about half an hour of waiting.

Today, however, the battery light remains on when the key is turned on and nothing happens when the key is turned to start. The battery has been replaced and the roadside assistance man was able to get it started by bridging a connection on the starter motor.

None of the dash lights besides the battery light illuminate when the ignition is turned to on, not even the service indicator.

Any ideas on what could be the cause of the problem?
December 1, 2010
  Followup from the Pelican Staff: Odd problem. I would start by checking the ground strap, and also check the resistance from the battery terminals to the power bus of the car and the ground. I'm not sure in 1989, but on many of the later cars, there was a "master fuse" or sometimes called a "fusible link" that broke / burned out if there was a short circuit across terminals in the battery. I would start looking in that direction. - Wayne at Pelican Parts  
m330xi Comments: when i start car cold makes a wiening noise till car worms up then stops sounds like bearring in alternator can i get bearing kit for it or just buy new one
November 28, 2010
  Followup from the Pelican Staff: If you have an alternator shop nearby, sometimes they can rebuild the unit with new bearings, but often it's just easier to replace the unit. - Wayne at Pelican Parts  
Thangamani Comments: 1.Alternator terminal voltages RN = 245 Volts
YN = 246 Volts BN = 245 Volts Measured with Digital Multimeter at No load
2.Generator Control panel input terminal Voltage Before switching ON OCB terminal voltages RN = 285 Volts
YN = 287 Volts BN = 267 Volts Measured with Digital
Multimeter at No load

While connecting a 20 HP motor Motor failed to run. How the voltages has been increased?. How it is possible? What may be the fault? How to check and correct?
November 15, 2010
  Followup from the Pelican Staff: No clue, this obviously is not an automotive application. - Wayne at Pelican Parts  
BMW Comments: BMW 1984 325e still having the same problem checkd for chassis ground looks good to me .but I order some new relay .just incase that's the problem.
November 14, 2010
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
Thangamani Comments: In the alternator terminal voltages are measured and found correct. But at the Control panelinput side side the voltages are increased by 20%. How it is possible? What may be the fault? How to check and correct?
November 14, 2010
  Followup from the Pelican Staff: I'm not sure. What were the voltage numbers you were measuring? - Wayne at Pelican Parts  
motoslipstream Comments: To hamish914

I had a problem with a "no alternator light " situation.

traced it to a by-passed alarm module ; hooked module back up and wala ! light back on !
Sincerely , vikingrat
November 14, 2010
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
Chris325e Comments: BMW 1984 325e Problem charging, new battery and new alternator car still dies.
November 12, 2010
  Followup from the Pelican Staff: I would check to make sure that the engine ground strap is attached to the chassis. - Wayne at Pelican Parts  
Hamish914 Comments: Alternator warning light doesn't light when ignition switched on.
Bulb works
12+ at D+ at connection to alternator
New Alternator and Regulator fitted
Eary strap connected on transmission
What should I see on DF? Should I see 12+ or earth?
Any suggestions as to problem?
November 7, 2010
  Followup from the Pelican Staff: Shoot. I thought I had my Bosch alternator book here at home, but I can't find it! If the alternator light is not coming on at start, then it sounds like it might be an internal diode problem. - Wayne at Pelican Parts  
Jamie Comments: 1988 911 Carrera. Do you recommend a rebuilt bosch or one of the new high output alternators $ ouch. I've not had any issues with the stock bosch until recently it is over charging and boiling the battery. Are there any marked advantages to the high output? Any reliablitiy issues with the rebuilts I've had problems with rebuilt starters? Sorry for all the questions.
October 27, 2010
  Followup from the Pelican Staff: Both are good quality units, just that one is rebuilt and one is brand new. We have gotten a few returns on the rebuilt units but none on the brand new ones. They are very nice. - Wayne at Pelican Parts  
roye mello Comments: hello wayne, 2nd hella reg gone bad, but 2 diff cars, good batts & gounds , never jump started bought forshop stock about 2 yrs ago. i installed a bosch reg & no issues - whats up with hella ?
hella part # 5dk00424115, 84 & 87 bmw 325's 80 amp
September 23, 2010
  Followup from the Pelican Staff: There's probably something in your electrical system that is causing these problems. It's not likely that the regulators are all bad, but they are probably being overworked or overtaxed (like the rest of us) and failing prematurely. Not sure what the problem could be, but the pattern is probably likely to continue. Maybe the alternator diodes are bad? - Wayne at Pelican Parts  
Handsome Comments: Sometimes the light comes on if I am cornering a bit too hard, I watch the guage real close when this happens. Sometimes it goes out by itself but always if I shut the car off and restart it. What do you think is going on?

Ian Stott
August 31, 2010
  Followup from the Pelican Staff: I wouldn't worry about it, at lower rpm, it's not uncommon to see the alternator lamp come on, particularly on older cars where the grounding isn't that great. I have a similar issue on my 1972 911. - Wayne at Pelican Parts  
peter Comments: my alternator is chargin but it is not chargin the battery
August 9, 2010
  Followup from the Pelican Staff: Have the alternator tested, have the battery tested, and check the engine / transmission ground strap too. - Wayne at Pelican Parts  
superman Comments: have you ever change the germanium diode in a rectifier bridge on a bosh alternator
October 5, 2009
  Followup from the Pelican Staff: Probably best to let a shop do this, or at least have them supply the diodes...- Wayne at Pelican Parts  

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