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911 Alternator & Voltage Regulator Removal/Replacement

Pelican Technical Article:

911 Alternator & Voltage Regulator Removal/Replacement

Wil Ferch


2-3 hours






1/2-inch socket, 10mm socket, 6mm Allen key, 8mm wrench or socket, 7mm wrench or socket, hammer, piece of wood, Sears Craftsman metric ignition wrench set

Applicable Models:

Porsche 911 (1984-89)
Porsche 930 Turbo (1986-89)

Parts Required:

Alternator, voltage regulator, six 8mm thread nylock nuts

Performance Gain:

A properly functioning and charging electrical system

Complementary Modification:

Replace your battery

I just completed the removal / replacement of the voltage regulator on my 85 Carrera. I'm posting this to the list as an aid to those who may go through this repair, or need to simply remove the alternator or fan assembly alone. The regulator is mounted to the backside of the alternator on the 84-89 models, and this procedure applies to those cars.

1.) Power down the system by removing the negative ( ground) cable from the battery. If you suspect an overcharging condition from the failed regulator (likely), now might also be the time to remove the battery entirely and inspect that area for acid damage due to a boiling battery. Paint / fix as necessary.

2.) At the engine, remove the A/C belt. Loosen  the 4 vertical bolts that hold the A/C to its mounting plate, and also back-off the jack screw (horizontally - on the right).   Slide compressor to the left, ease belt off of pulley. Note: these are not metric bolts. These are 1/2" head, not 13 mm. Most Porsche A/C hardware is not metric.

3.) Loosen fan belt . Keep track of the shims ( I had 6 shims total), and note the number of shims under the pulley, and how many were on the outside. Use all the shims when you put the belt back on later. You will damage the alternator shaft if you don't use the proper number of "outside" shims to get to the 6 total.

4.) Locate the ignition wires running on top of the fan shroud. There are two, 10mm ( head) bolts that secure the wires into the fan shroud, at about the "11 o'clock" and " 1 o'clock" positions . Remove these bolts.

5.) Remove a similar bolt at the "9 o'clock" position on the fan shroud, near the distributor. This is a shorter version of the other two. Don't mix them up.

6.) Remove the allen bolt ( 6mm allen wrench) securing the large fan strap that holds the fan housing in place. Push the ignition wires back, and "lift" ( bend ) the strap up, to gain access for the next steps.

7.) Pull alternator "out" toward you. It will move only a small amount, until the fan housing contacts the back side of the crank-mounted fan pulley. Wiggle / tilt the unit until it comes out further- restrained only now by the attached wires. The housing will "just" clear the fiberglass shroud. You now face a small "wedge" opening at the top (between the housing and the shroud) that you will need to do your work. Patience and small hands are a plus.

8.) A funnel-shaped"air duct" with vanes,  is attached to the back of the alternator. It is attached by three , 8mm ( head) nuts on the backside of the alternator. These 3 nuts are in a  "staggered" arrangement with 3 other nuts on the alternator backside (6 total). We won't worry about the other 3 for now- can't access them anyway. We're only interested in the 3 that remove the air duct. Do this carefully, there isn't much space, and there's a good chance of losing the nuts/washers. Take your time , and take breaks, if necessary. Separate the air duct from alternator ( push air duct back).

9.) The regulator , and mounting wires should now be in view. Remove wires, noting their positions. From your  viewing vantage point (from fan end of alternator), with the regulator on "top", the red wire was at the bottom, blue to left, brown ( 2 wires)  to right. Note that the red wire uses a 10mm head bolt, brown uses 8mm, and blue uses 7mm. I guess this is supposed to help us, if we don't remember the wire locations (!).

10.) Now the entire cast fan housing , with attached alternator, can be removed from car. If you're only going to replace the regulator, your'e there. The regulator is held on by two, 8mm bolt heads. Note yellow and blue spade connectors and their locations, and replace. If you want the alternator removed for refurbishment (advised), continue to next step.

11.)You will now note the "other" three, 8mm head nuts ( that you couldn't get to earlier when removing the air-duct). These 3 hold the alternator to the cast fan housing . Remove these 3 nuts, noting their location [ that is, whether or not they were included in holding the air-duct funnel. I used this approach: the nut that straddled the regulator centerline DID NOT hold the air-duct funnel. Every "other" nut ( in a staggered, 120 degree pattern) also DID NOT hold the duct. The remaining three DID hold the air duct. Alternator will likely be "frozen" to the housing. With caution, use a hardwood ( or such) to tap on the 6 bolts to get it out. I even used heat from a hair drier to "expand" the housing, which helped.   Patience ! Go in a circular pattern. I used a metal hammer, which worked, but I "flattened" the end of the bolts slightly causing grief when re-installing the nuts.Don't do this !

12.) Next is fan removal. Likewise, it will appear frozen to the shaft. Support the backside of the fan in the corner of a wooden box ("blocking the fan"), and allow clearance for the alternator to fall out ( not too far!) Allow maybe 2 inches of drop HEIGHT and place cushioning material underneath). Tap fan shaft end with hardwood block , and unit should drop out. Don't loose the shaft key.  Alternator is now out for repair, which a local shop did for me for $75 ( new bearing , slip rings, and bench testing).

Re-installation is the reverse of the procedure.

Some observations:

1.) I used anti-seize on the fan shaft , and the mating surface of the cast fan housing "bore" that accepts the alternator. This should help keep the units from "freezing" together again.

2.) I bought new 8mm head ( 5 mm thread) nylock nuts for the 6 nuts on the backside of the alternator. Just added insurance.

3.) When re-attaching the wires, don't just note the proper mounting locations. Also try to locate the wires radially inward as much as possible. This helps later air-duct- attachment.

3.) When re-attaching the air duct, you can "rotate" the fan / housing / alternator ,so your "work" ( in re-attaching nuts)  will always be "on top". I believe there was a lot of rotational "give" in a CCW rotation , and not that much CW. Experiment. Rotate back to original position to continue the installation.

4.) Re-installing the cast housing into the fiberglass shroud will again be difficult. Lifting and tilting before re-entry is advisable.

5.) Push housing back as far as it will go. There is a "peg" on the engine part of the fan support , that locates the 6 o'clock position of the housing. Make sure it is engaged properly. Done right, it will allow only minor movement laterally (rotationally). Fasten strap to tighten completely.

6.) Often overlooked. If your battery had boiled due to a failed regulator, I wouldn't just add water and re-install. The car's electrical system is meant to keep the battery "at charge", it wasn't meant to get it there from a low condition. This puts undue strain on your electrical system. Better, to trickle charge your battery while it's out of the car ( while you're doing the repair), and put it back-in fully charged and ready to go.

Hope all this might help someone!


Wil Ferch- 85 Carrera

Addendum: With all the thought I gave to writing this, I noticed that I forgot to mention the usefulness of  a small, "ignition wrench" set sold by Sears/Craftsman.  These physically small wrenches really helped in the tight nether regions of the area.

Also see Wayne's write-up on this topic as well...

Comments and Suggestions:
gptom Comments: the ground strap was mounted to the 2nd bolt instead of the 1st. that's why not enough slack. thanks for your help
July 30, 2016
  Followup from the Pelican Staff: UGH. I wish I thought of that being the issue. Thanks for the follow up, much appreciated. - Nick at Pelican Parts  
gptom Comments: well, the case nut is out, per Ed Mayo the assembly is on my bench

I am now at the point trying to remove the alt from the vane,

how hard can I pound on the 6 screws? I have Kroil on for overnight soak
July 16, 2016
  Followup from the Pelican Staff: You can't pound very hard, as the housing can break. If the screw heads strip, try cutting a straight slot, then using a flathead screwdriver. - Nick at Pelican Parts  
gptom Comments: It's not the harness, there is a little bit of slack. Ground strap is by itself and that is what is holding the alternator from rotating
July 13, 2016
  Followup from the Pelican Staff: Ok, then you will have to find a way to loosen the fastener. I haven't had this much trouble before, maybe yours has been shortened. - Nick at Pelican Parts  
gptom Comments: That would mean taking a case nut off. Is that OK to do? I'm sure that I won't be able to use a torque wrench to reassemble
July 12, 2016
  Followup from the Pelican Staff: If you can't torque don't, avoid removing case nuts.

Can you make slack somewhere in the harness? - Nick at Pelican Parts
gptom Comments: I have a 72 2.4 MFI. I cannot get the alternator to rotate because of the alt to block ground strap. I cannot remove the last 2 nuts. any suggestions?
July 9, 2016
  Followup from the Pelican Staff: Can you free the ground strap on the opposite end to allow it to move more? - Nick at Pelican Parts  
Frank Comments: Hi, I have an 89 911, 3.2 Targa.

Just had alternator rebuilt locally. Tested at shop after rebuild and it works fine. Reinstalled and rewired everything correctly. Belt is spinning the alt/fan fine, no slippage. Voltage at battery BEFORE startup is 12.25, after startup is 11.7, regardless of RPMs. Battery light on. Replaced battery with a brand new one. If alt works, then the problem is the wiring in the car that isn't allowing a charge, right? Or is there a fuse that could be blown? What am I missing?
March 23, 2015
  Followup from the Pelican Staff: What was voltage and amperage output of alternator when tested? I have seen many new or rebuilt units still faulty.

The circuit is simple.

Brown wire ground.
Blue wire battery volts with key in On position.
Red wire battery volts.- Nick at Pelican Parts
MarkArnold Comments: on my 1973 911E and probably others there is a ground strap on the bottom bolt of the alternator to fan housing bolts. Undo it first and it will make life easier. If your car does not have a ground strap from the alternator to the engine it is not a bad idea to add one.
September 19, 2014
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. - Nick at Pelican Parts  
K_fed Comments: Just a follow-up. the new regulator resolved the headlight and dashboard flickering problem. All is well!
September 30, 2013
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
busker Comments: Hi , i am trying to replace the regulator on my 81 sc. it is located on the left rear wing inner not part of the alternator. It looks easy enough but I cannot get the plug connector to release. Any tips please.
Thanks Mike
September 24, 2013
  Followup from the Pelican Staff: Can you share a photo of the connection you are having trouble with? If you are having trouble with the slide on female spades, they can get stuck. Try working them off gently and slowly using a small flathead screwdriver.- Nick at Pelican Parts  
K_fed Comments: I too was getting a flutter in my headlights and dash I don't run any high-power amps or anything. I bought a device that plugs into the lighter socket with a digital voltage readout and it showed my voltage fluctuating up and down at any RPM11.9v - 16.5v. Suspect that this may be the culprit to my light problems, I installed a Valeo regulator and it sits at a stable 14.05 volts. Have yet to test the headlights out at night to see if it's resolved with the regulator-but I'm hopeful! I did notice in the Valeo instructions, it shows a metal tab/terminal to install. It looks to be installed on the right side of the alternator when looking at it from the back. I found no further information anywhere describing the purpose of the tab. I attached the leads where the old regulator was and left the tab out. Has anyone else run into this situation? See attached diagram from Valeo-Step 4b. The diagram was poor to begin with but it gives you the general idea. 87 Carrera, 62k
August 26, 2013
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
zippy_gg Comments: Great write-up and right on Wil!
I just disassembled the fan/alternator on my 86 Carrera cab this evening and here is my small contribution:
Blue wire held by 7mm nut and washer, 2 brown wires 1 thick one attached to one of the engine bolts for ground, 1 thinner one goes to the harness held by 8mm nut and washer, 1 big red wire held by a 10mm nut and washer. Alas it was too dark to take pictures during disassembly.
December 30, 2012
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. - Nick at Pelican Parts  
s_chev Comments: Thanks for documenting this Wil. That was probably a few years ago, but I just printed it and followed it. Spot on. I appreciate it.
June 14, 2012
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. - Nick at Pelican Parts  
shuzboomer Comments: What is a good place to hook up a meter in the engine bay to troubleshoot an overcharging or voltage regulator problem?

Thanks in advance

January 17, 2012
  Followup from the Pelican Staff: You can work at the battery terminals. This is a good place to test the charging system. If you want to check in the engine bay, you can connect to the battery positive junction and engine ground. - Nick at Pelican Parts  
jlcinga Comments: Thanks for the great step by step...really helped.
I learned a couple of things:
My fan was firmly stuck on the shaft....tapped a couple of the 16 holes around the fan hub and easily forced it off with a couple of bolts...alternately tightening them.

Alternator would not come out of housing even with vigorous tapping on the six bolts. I took three of the long bolts out alternate ones...from the shaft side and inserted three sacrificial bolts from the side where the six studs stick out. This gave me three bolt heads to beat the hell out of...alternator came out, but still was reluctant.

Thanks again for the good write-up.
July 24, 2011
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. - Nick at Pelican Parts  
olliey Comments: hello read about the removal and replacement of the alternator. I have quick Question. I was wondering how would you be able to trace the wires coming back from the alternator to the front of a porsche of a 1982 911 and the problem is that the hazard lights arent working they work when they want to but it seems like it has a short what should i look for
November 28, 2010
  Followup from the Pelican Staff: Hazards not working? I would check the hazard / flasher relay, as these often fail over the years. - Wayne at Pelican Parts  
brd Comments: Thanks for the write-up.
A small note... if you are too enthusiastic with the hammer using a block of wood of course when trying to release the fan from the alternator shaft, you can knock out the bearings on this shaft from the alternator housing itself. Better to go slow and steady.... oops.
July 24, 2010
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. - Nick at Pelican Parts  
lovemybabyblue Comments: Anyone have a similar guide for how to remove an alternator for a 2002 911 Targa?
May 2, 2010
  Followup from the Pelican Staff: I've got one coming soon. In the meantime, the 2002 Carrera alternator is almost the same as the Boxster one. Here's the link to the article on the Boxster alternator replacement: - Wayne at Pelican Parts  
Jack Comments: Sorry Guys....I just read the... Wil Ferch- 85 Carrera Story...That will help....I Should have read that first
February 23, 2010
  Followup from the Pelican Staff: Thanks for the input on this one. - Nick at Pelican Parts  
J.Paul Comments: Thanks. It worked perfectly, however, I'm still getting some flutter with my lights and dash. I'm pushing a couple of amps for my stereo and I am now wondering if that is the problem. Is there an upgrade or something that I can do for this challenge. 1985 911 Carrera Targa, 130k.

July 6, 2009
  Followup from the Pelican Staff: If you unplug the amp, do you still have the same problems? Issues like these are also often caused by poor ground connections, I would check them all, especially the transmission ground strap. - Wayne at Pelican Parts  

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Page last updated: Mon 1/15/2018 02:25:06 AM