Electrical Repairs Troubleshooting 1980 US

[aluminum]

Hello All :
Well after a bit of Mechanical Repairs I got My Long time Sitting ( 15 Years ) 1980 US Running
928 5 Spd running Very Good . I am surprised at the Handling and Power of the early 928 . Much better then I had Hoped for .
Now time to try for the electrical as Lot's does not work .
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What's Working :
Car Starts and runs fine Hot or Cold
Headlights / taillights / Stoplights / Running lights / License Plate Light / Turn signals
Battery Charge Gauge / Temperature Gauge / Heater and fan / flasher / Rear Window defroster
**************
What's not working :
No Dash Lights / No Speedometer / No Tachometer Central Warring System Light always on ( Center of pod ) Central Warring System Light on also in center consul
Oil Pressure Gauge always Pegged past 5 to the top motor on or off but with Key on.
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What's been Done Electrical : ( Testing )
As A Test I removed the 2 wires to the Oil Sender Turned Key on ( motor off ) and the Gauge still Pegged > Same with it started . It Peg's so hard I have to tap the dash with the key off to get it to drop back to Zero.
Hooked it back up and removed Pin 2 and 4 ( oil Pressure )from the 14 pin connector > still peg's when I turn on the Key or start the car . So ? I expect the short is before the 14 Pin Connector then Correct ?
******************
Pulled the Central Warring system enclosure from under the dead pedal and found it has several burned out areas ( resistors / shorted out circuits . The boards where showing bad signs of moisture damage / Green and white corrosion .
Decided it was not worth repair I well just replace it with a good one.
I did Note ! that after reinstalling it ( I did clean it up a bit and the connections )
2 things (1)when first starting the car the warning signal went off for the first time for a few seconds .
(2) Also Noted that without bolting it down the warning signal did not come on at all
I assume as it was not grounded .
So perhaps replacing Central Warring system Unit may solve that Problem .
***************************************
All fuse's and the board are clean and in good condition > I pulled and cleaned the board
where should I start ?

Thanks in advance for any advice or Hints
( certainly helped me with the timing belt and water Pump Issues . )

[riber.bentsen]

No dash lights is probably the dimmer that has corroded. Remove the black plastic cover under the pod and short the wires that go to the dimmer. You won't ever need a dimmer on these lights, trust me!

Mine does the same with the oil gauge, have to tap the pod to get it down. I'm looking forward to your findings, I will start with replacing the sensor next oil change..

No speedometer, hmm. I don't remember if these early cars have electronic speedometers. If that is the case, try removing small black plastic cover in the spare wheel well. There would be the connector for the speedometer. (It picks up from the diff.)

[MPDano]

Like Riber said, pull the wires off the Potentiometer (spelling?) which is also the dimmer wheel. Put 2 spades on a wire and just jump it. As far as your Instrument Cluster issues, most likely the PCB (Printed Circuit Board), which I bought from 928 Intl. Solved all issues with that. You might be lucky and it's just a couple circuits on the legs where it connects with the harness connectors. Here are some pics where did an overhaul of the Cluster:

Porsche 928 Forums dot com - View topic - Pics of my First 928 and Current Project

[aluminum]

Thanks Guy's
I well look into those area's and for the Dimmer under the pod Also for the Cover in the spare tire well ? ( don't remember seeing that ? )
I understand about bypassing the dimmer and direct wiring the Dash Lights I can do that no prob.
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Some Stuff works their > like the Parking Light indicator ( when on ) High Beam Indicator Light .
My 911 has the same problems in general IE: ongoing Electrical Problems .
**********************
Hoping to get more working so I can take it in for SMOG >> ha ha can you believe it I was a SMOG INSPECTOR (1966) and all they had was a PVC Valve and a bunch of Hoses and the Air Pump started ha ha >> GM sent me to a 2 week school > Evan paid me during the classes.
*******************
Just a Side Question ? does the Tachometer run off wires to the Distributor ? >>
You know I am thinking that Perhaps their is a Bad connection to all that stuff as their is so much out ?> The Wiring and Insulation Look's GREAT with the exception of some Hard stiffness on some of the Bundled Wires under the hood ( from Motor compartment Heat )
I shall update my findings > So far the Only Bad Wiring itself seems to be in areas of Pin Connectors like the Brain / the Central Warning System Box / 14 Pin Connect > and the like > But not the wires themselves . I expect however I just have not found some bad wires yet . I did notice that the most Corrosion is in areas of Dampness ! When these Car's sit water gets on the floors and the Dampness creeps right up toward many electrical parts.

[JhwShark]

Originally Posted by aluminum

Thanks Guy's
Just a Side Question ? does the Tachometer run off wires to the Distributor ? >>
You know I am thinking that Perhaps their is a Bad connection to all that stuff as their is so much out ?> The Wiring and Insulation Look's GREAT with the exception of some Hard stiffness on some of the Bundled Wires under the hood ( from Motor compartment Heat )
I shall update my findings > So far the Only Bad Wiring itself seems to be in areas of Pin Connectors like the Brain / the Central Warning System Box / 14 Pin Connect > and the like > But not the wires themselves . I expect however I just have not found some bad wires yet . I did notice that the most Corrosion is in areas of Dampness ! When these Car's sit water gets on the floors and the Dampness creeps right up toward many electrical parts.

Tach comes from G7 on CEP, which comes from CEP O7 to Pin 16 (on a plug) on the TIU...so you should inspect that plug as well as the 14 Pin top harness wires inside the wrap they are/may be degraded as they pass over the front and down past the dizzy.

[928_Owner]

Hi aluminum,

I started another thread a couple of weeks ago about the faulty oil pressure gauge. I still have not got it figured out yet. My situation is a little bit different than yours. My oil pressure gauge works for a few minutes then goes to max. From my testing using a digital volt meter (DVM), I've determined that when the oil pressure gauge is reading max, the circuit to the oil pressure sender is OPEN, not shorted to ground. I'm beginning to suspect that the issue in most likely in the instrument cluster itself. I'm going to dig into it this weekend.

Keith

[JhwShark]

Originally Posted by 928_Owner

Hi aluminum,

I started another thread a couple of weeks ago about the faulty oil pressure gauge. I still have not got it figured out yet. My situation is a little bit different than yours. My oil pressure gauge works for a few minutes then goes to max. From my testing using a digital volt meter (DVM), I've determined that when the oil pressure gauge is reading max, the circuit to the oil pressure sender is OPEN, not shorted to ground. I'm beginning to suspect that the issue in most likely in the instrument cluster itself. I'm going to dig into it this weekend.

Keith

Keith,
Have you inspected the Oil wires (from pin 2&4) inside the 14 pin top harness...not at the connector but down the harness a couple of feet. They may be degraded and causing an open (shorting happens there as well) as the car heats up...many have had similar issue forcing a re-wire.
Jon

[928_Owner]

Originally Posted by JhwShark

Keith,
Have you inspected the Oil wires (from pin 2&4) inside the 14 pin top harness...not at the connector but down the harness a couple of feet. They may be degraded and causing an open (shorting happens there as well) as the car heats up...many have had similar issue forcing a re-wire.
Jon

Hi Jon,

I replaced the 14 pin plug and wiring harness (the part that goes to various places on the engine, including the oil pressure sender) a couple years ago. That harness was a real mess, the insulation disintegrated on most of the wires. The other half of the wiring harness (from the socket that is attached to the body), I have not investigated, yet.

Keith

[JhwShark]

Good to know...the other harness is a bit more to deal with, though I have not had to yet.

I'll look for updates to your oil thread...
which side of the Bay?? I'm on the peninsula side.

[Landseer]

Well, its really good news to hear you got this car running so well so quickly. Congrats! Hope you plan to keep it, it will be fun.

Clean all grounds first, if not already done.

Then because interior lights and dash lights share circuitry, I'd pull down the ceiling and hatch light fixtures to inspect for harness integrity, same with door lights and make sure door end lights are working. Lots of time these fixtures short on the body, often after a car is resurrected. Use extra heat shrink if needed to protect. Check fuse again. Potentiometer under pod could also be issue, as stated, and it can be bridged.

Then, I'd pull the pod and carefully inspect the circuit board and clean the three board attachment connectors. And I'd probably install an new OEM ignition switch electrical portion from a known supplier.

I'd scrutinize every wire on every plug on the CE panel, and behind it, and especially in the console area under the radio, looking for any/all scorches and melts as telltales --- If you spot one you must trace the line pretty much visually, even it it means unwinding the harness wrap.

This process, along with CE panel polishing and new fuses, is how to prep for any further item by item deep dives that might be needed.

[aluminum]

Well I did have time to pull the Pod today and "MPDano" WAS RIGHT (Thank you ) the dimmer wheel was bad > shorted out on one spot.
However Lot's of bad Electrical all over However the wires themselves look ok ? ( I am surprised at this )
It's strange but the power to the dash lights Dimmer comes on when the Key is turned on ? rather then when you turn on the Lights ? " That can't be right " can it ?
A few bulbs are burned out 4 I think > the Spedo and Tac are electronic both don't work.
Printed Circuit Looks perhaps ok but dirty . a few wires have been hacked into I see hummm
Repaired the wiper intermittent Control also a wheel controlled unit > soldered it where the original was just Crimped together.
I have to leave town for a few days but shall get back to it in say a week >
Well try to pick up a Central Control Unit in the Bay area also perhaps a Instrument Cluster if I see one that looks good . I noted the 2 screws where lose on the back of the Ignition switch and tightened them up.
I see their are 3 Main wire harness hookups to the Instrument Cluster and they in fact are marked as to just what each one is ( in German ) ya ya
I noted something seems missing on the back of the Tac ? I expect I well have a look at some of them in the racks in Hayward Ca a Porsche salvage Yard as they owe me some money and I need to stop by their anyway salvage Yards are Kool as they let me roam around in them for some reason ? ( and this is a Porsche yard ) . I know many people don't like used parts but some used parts are ok and this is no show car that's for sure > But darn it sure drives great !!!!!
I really Don't like Electrical Issues but well do my best humm am already thinking to get Oil and Temperature gauge set perhaps .Porsche Electrical is not on my XMAS list however and I expect a real Oil Pressure Gauge would be nice rather then a electrical one . I kind of like the idea to know just what the real Oil pressure is and yes I know Its High humm perhaps their is a better place to hook one up rather them right at the electrical sender area ?
Wow lots of good tips I an reading here to look into when I return from my Work trip for a few days
Thanks everyone it sure makes it much easier as electrical issues are the hardest for me . No doubt this well be a lot of work but we shall see.

[MPDano]

Fun stuff, eh Aluminum? The feeling of fixing something you've never tackled before is awesome. Keep going and good job. PCB's were $100 at 928 Intl when I bought mine. I think someone said they were NLA, but call them and find out as once their gone, their gone.

[aluminum]

Originally Posted by Landseer

Well, its really good news to hear you got this car running so well so quickly. Congrats! Hope you plan to keep it, it will be fun.

Clean all grounds first, if not already done.

Then because interior lights and dash lights share circuitry, I'd pull down the ceiling and hatch light fixtures to inspect for harness integrity, same with door lights and door end lights. Lots of time these fixtures short on the body, often after a car is resurrected. Use extra heat shrink if needed to protect. Check fuse again. Potentiometer under pod could also be issue, as stated, and it can be bridged.

Then, I'd pull the pod and carefully inspect the circuit board and clean the three board attachment connectors. And I'd probably install an new OEM ignition switch electrical portion from a known supplier.

I'd scrutinize every wire on every plug on the CE panel, and behind it, and especially in the console area under the radio, looking for any/all scorches and melts as telltales --- If you spot one you must trace the line pretty much visually, even it it means unwinding the harness wrap.

This process is how to prep for any further item by item deep dives that might be needed.

Thanks Landseer : I well check out those area's when I come back from the bay area >Overhead lights Etc . I also have the door panels off and all the wires hanging from them Etc. The dash Lights and Gauges where out before that however.
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I stopped by Santa Rosa and looked at a 79 and a 83 ( the 83 was advertised as a 86 ) Both more or less junk > the 83 is a S a 5 Spd > I passed on them but you never know until you look.
Thanks and have a great weekend

[stepson]

Originally Posted by landseer

clean all grounds first, if not already done.

+928