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Technical & Safety: Electrical System Upgrades
 
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Pelican Technical Article:

Technical & Safety: Electrical System Upgrades

Lee Rice

Time:

2-4 hours

Tab:

$50

Talent:

***

Tools:

Metric socket set, Philips and Flathead screwdrivers, floor jack, jack stands, flashlight, inspection mirror, soldering iron, solder, electrical tape, heat shrink tubing, wire cutters.

Applicable Models:

 
Porsche 911 (1965-89)
Porsche 930 Turbo (1976-89)
Porsche 964 Carrera 4 (1989)

Parts Required:

Gang double fuse block, electrical wire, blue 25 amp fuse, red 16 amp fuse.

Performance Gain:

Reduce load on electrical system.

Complementary Modification:

Replace starter with 1.5 HP starter upgrade.

Electrical Problems

     Customer complaints from non-functioning air conditioning, fuel pumps that don't work, and smoking melted wires and relay sockets. Even fires have been evident in standard everyday Porsches. Why? For most of us with older, pre-1990 Porsches, we need to be aware of the electrical loads imposed by the Porsche factory that never really re-wired the Porsche line - they just kept adding each new system on top of the already cramped and overloaded original system. Porsche owners have installed radio! tape/disc players and amplifiers and extra disc storage drives. Then there are those improved lighting systems, alarm systems, and radar/laser detectors, car phones, lap tops, battery chargers, etc. The list can be extensive and that is a real problem for the older Porsche. As an example, my 1968 911 is probably one of the most modified prototypes in the world. I have changed ... everything! One common link to every other Porsche out there is that my 911 had the original wiring system. When the upgraded C-2 air conditioning system was installed, I knew the wiring was stressed beyond its capacity, and the A/C wiring was upgraded then.

     Last month, I wrote about the replacement of the original starter-battery cable. That very noticeable improvement led to looking closer at the rest of the system. I found that the factory used one cable to connect the battery to one connection on the fuse strip. From there, power supplied to two or three other connections on the fuse block. All of these are connected on the same side of the fuse block. These three connections (three gang) would not run power through the fuses but would supply three individual connections to supply power to other systems. The problem with this is in the fuse block itself.

     The fuse block uses small brass strips that are riveted to each other and the fuse terminal. When high current loads run through these strips, they generate heat. Heat expands each part a little bit and as one strip expands more than the others, it moves and loosens with use and time. Severe fatigue results in smoke, melting wire insulation, and fire. 930 Turbos with two fuel pumps, and all the warm-up gadgets on the engine, simply over tax that system. Most of the 930's have had at least one fuse block replaced.

     I have removed some of the original battery feed cables that went directly to the fuse block and I have them run directly from the battery to each of the major power systems. The following is a simplified select few areas that can be upgraded with a few hand tools and a wiring diagram.  [Click Here for the Wiring Diagram Figure]

Air Conditioning System -911 and 930, 1969-1989

     The objective is to remove a major electrical load from an already cramped and over stressed single fuse (~16) by redirecting direct battery power to two independent fused supplies. Install a new two gang double fuse block Nr. 911.612.085.04 ($17.00) near the standard fuse/relay panel. Disconnect 1.5 red/green wire at fuse #20 and attach it to new fuse block terminal #1. Install a red 4.0 cm/2 wire to the battery + terminal. Run this wire to the new fuse block and solder the end so that the screw that secures it to the fuse block will not work loose. Attach to the two gang interconnected end. Install a blue 25 amp fuse in each fuse holder and install the fuse cover. Now you have a separate circuit independent of each other. The fuse block will be cooler and not overload the rest of the system.

Ignition and Light System -911, 1965-1969

     This system always seems to be overloaded and the switch and wires feel warm when in use. Disconnect the heavy red wire from the fuse strip. Using new 4.0 cm/2 red wire, solder the new wire to the old and securely heat shrink the connection. Avoid crimping connectors! Run the new wire to the battery + connector and attach.

Fuel Pumps on 930 Turbo, 1977-1989

     Both fuel pumps take power from one fuse (#16). Install a two gang fuse block, Nr. 911.612.085.04, near main fuse strips and run a red 3.0 cm/2 red wire from the battery terminal directly to the new fuse terminal, at the two gang end. The two fuel pump relay sockets for pump #1 and #2 have a red wire 2.5 cm/2 running from fuse #16 to terminal #30 of pump #2 and then run over to terminal #30 of pump socket #1. Cut the wire running between the two pins, #30, and securely splice it by solder and good insulation to a new 3.0 cm/2 red wire, running it to the new fuse block at #2. Be sure to solder the wire end before installing it to the fuse block. Remove the red 2.5 cm/2 wire from fuse #16 and run it to the new fuse block and attach it to the #1 fused terminal. #2 fuse should be a blue 25 amp, as it will still power the warm-up devises as well as the #2 fuel pump. #1 fuse can be a red 16 amp fuse.

These are a few simple upgrades that improve your reliability and safety. This upgrade takes less time to install than to write about it!


Lee Rice writes the monthly Technical & Safety column for the Orange Coast PCA(zone 8) Newsletter.  He has generously allowed Pelican Parts to republish these articles here for the benefit of everyone who visits the site.

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Comments and Suggestions:
Stathis Comments: Hello, I have a 1970 911T targa. The car has been restored completely from 0 but, I stuck on the electic part. The colour code on the wiring diagram downloaded from Internet is not matching with the reality. I would appreciated any help or any wiring diagram close to the model
December 1, 2016
griff Comments: I need a wiring diagram for a 1986 porches 928s on fuses a chart please
January 11, 2016
  Followup from the Pelican Staff: I don’t have that info.
I would grab a repair manual.

Give our parts specialists a call at 1-888-280-7799 - Nick at Pelican Parts
 
maninblack Comments: Good stuff here. One correction. Regarding Turbo fuel pumps it states "Fuel Pumps on 930 Turbo, 1977-1989, 1976 used a single pump". This is incorrect. 1976 Turbos have both front and rear fuel pumps.
September 29, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 
Tachi Comments: What kind of instruments do you need to retrieve fault codes
on 1991 Porsche 911 Turbo ?

I notice by passenger right inside a round plug?

Joe
July 14, 2015
  Followup from the Pelican Staff: Durametric should do it. - Nick at Pelican Parts  
Bud Comments: Question: Is a 1986 main wire harness the same as a 89. 2.7 liter car?
May 21, 2015
  Followup from the Pelican Staff: No, I don't think so. You can check the part numbers against each other to be sure. - Nick at Pelican Parts  
mike Comments: also my car radio shuts off and then on.... at the same time the fasten seat belt comes on .any idea..?
May 21, 2014
  Followup from the Pelican Staff: Sounds like you have multiple electrical faults. I would start by checking the vehicle for fault codes. There may be a fault for a power circuit / relay. This could direct you to the course of the issue. - Nick at Pelican Parts  
mike Comments: mercedes benz.....
May 21, 2014
  Followup from the Pelican Staff: OK. got it. - Nick at Pelican Parts  
Mike Comments: Is there any way to get the actual chart for the fuse box cover?
May 18, 2014
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. If they can't find it. Mercedes-Benz should be able to. - Nick at Pelican Parts  
mike Comments: i need to get a fuse chart diagram for a 1986 Porsche 911 targa any idea where
May 13, 2014
  Followup from the Pelican Staff:
I would grab a repair manual. It should have that info.

Give our parts specialists a call at 1-888-280-7799 - Nick at Pelican Parts
 
delta911 Comments: I INSTALLED THE 2 GANG FUES BLOCK RAN THS WIRES TO THE FUEL PUMP RELAYS ON MY 87 930 TO THE #30 PINS ON BOTH RELAYS AND CUT THE JUMPER BETWEEN THEM ... NO THE CAR WONT RUN THE RELAY SOCKETS ARE NOT THAT SYMPLE AS IN THE DIAGRAM THEY ARE COMPLEATLY COVERED IN RUBBER THERE IS MORE THAN ONE RED WIRE . DID I USE THE WIRE TO PIN #30 or what if i used the wrong wire what would be the outcome ??? THE CAR WILL START RUN FOR A SECONDS AND DIE... I NEED HELP .... THANKS
June 19, 2013
  Followup from the Pelican Staff: Terminal 30 should be constant power. Is that what you have there? I can help you with a little information or some pictures of what you are doing. - Nick at Pelican Parts  
BH27 Comments: '86 911, can barely see the dash lights, the stereo balance pot is definitely in need of cleaning, and wiper switch only works in the slow position when you jiggle it. I thought all probably needed cleaning but do you think pulling a larger power wire to lights could help that issue?
January 4, 2013
  Followup from the Pelican Staff: I would check the ground before you add a power wire. - Nick at Pelican Parts  
JR Comments: Where is the a/c receiver dryer located on a 1991 Porsche 930 coupe???

Can't see it under any fender. Anyone know??
behind some panel?

Joe
July 6, 2011
  Followup from the Pelican Staff: If I remember correctly, is it mounted in the rear of the left front fender. - Nick at Pelican Parts  
bigt Comments: I want to replace the fuse panel on my 1983 944...any hints?
March 1, 2011
  Followup from the Pelican Staff: Once you locate one. Unbolt it, pull it down, then swap the wires and connectors over. - Nick at Pelican Parts  
Lou Comments: Is it normal for the a/c switch to get hot when in the on position?
July 20, 2010
  Followup from the Pelican Staff: I'm not sure which car you're talking about, but if there is a light bulb inside the knob of the switch, then it might get a little warm, but it shouldn't get hot. - Wayne at Pelican Parts  
big H Comments: WHERE CAN I FIND GLASS FUSES FOR MY 1976 911. THE CERAMIC ONES TEND TO CORRODE TOO EASY.I FOUND ONE THAT HAS A BUBBLE TYPE TIP ON THE END THAT WORKS, BUT NO MARKINGS AND I CAN'T FIND ANY MORE. A FRIEND HAS SOME IN HIS VOLVO AND HE CAN'T REMEMBER WHERE HE GOT THEM. PLEASE HELP I'M DESPERATE!!!!
January 8, 2010
  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
 
Terry Comments: Doing the impossible. I purchased a wrecked 83 911 SC to use to rebuild my original 1976 Targa purchased in Europe Euro specked. I wanted the air conditioning, the brake system vacuum assisted, the engine which has the computer controls. Mine had become an oil pump. Now I have a million problems. I changed the wiring harness and have been trying for the last 3 months to figure out all the wiring. I still have wires that go no where. The defrost switch and the driving light switch is dring me crazy also. The wiring diagrams I have seem to conflict. I now have a fuel pump sitting in the front and another that is in the back that requires power. Do you know of anyone that has a layout of the wiring harness Pictoral that shows the cables in place. I took a ton of pictures but it is imposssible to figure it all out even with the pictures. I think I have about 88 percent of the wires in place on the instruments. But I need 100 percent before I put all the air ducting and windshield wipers back in. Help!!!!!
April 21, 2009
  Followup from the Pelican Staff: Crazy complex job. Too much detail to discuss here - you should post for help in the 911 Technical Forums - http://forums.pelicanparts.com/forumdisplay.php?f=8 - Wayne at Pelican Parts  

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