928 Electrical problems

[1979928]

I am trying to find some help from the 928 community. I have a 1979 928. My alternator went out a few months back. I ordered a rebuilt unit and the car seemed to be doing fine. Among the other problems, I was having a faulty high beam switch which I replaced with a used one. When I replaced it, my dash gauges, mainly my speedometer, was reading my battery charge which dwindled down to nothing. My fuel and temp gauges are pegged out at the max. I suspect that something is grounding out on the dash circuit board, but I’m not sure. I am hoping that someone can shed some light on this problem so I can buy some parts and fix the problem. I know that that chance of someone being able to figure it out without ever seeing it is unlikely, but I am willing to accept any help that anyone can give. It’s a fun car when it’s running and I miss driving it. Thank you in advance for any help you can give.



Ty

[Danglerb]

Measure the voltage with a real meter, could be the rebuilt has a bad regulator. I'd say check it at the jump post in the front and at the battery.

[1979928]

I guess I need to elaborate a little more on the problem. After I replaced the alternator, I ended up replacing the high beam swich since it indicated that my high beams were always on and would not let my fog lights ever come on. The alternator only stared to go out again after I installed the switch. I thought that I may have installed a bad switch causing the problem so I unhooked the switch and out my old one back in there. Neither the new used switch or the old switch made a difference with the high beams either. Relays have been checked and the whole nine yards. One guy from 928 Intl suggested the circuit board behind the dash may be faulty and grounding out. Ever heard of such a thing and what arte the chances it can cause an array of small electrical problems with headlights and charging. I just figured something has grounded somewhere blowing the voltage regulator again. Like I said in my main post, I am williong to try about anything. I've had 911's and everything else in between. In fact this is my 8th Porsche, but I have never seen one come fully loaded out and with so much wiring. It is almost scary when you go to track something down.

[Danglerb]

If the alternator is putting out too high of a voltage, I 'm not sure anything external could cause that. Anybody know if replacing the charging bulb/resistor to the exciter "wrong" could cause this, or some kind of short?

What area are you located in, maybe we can stir up some local help?

Put some spaces in that monster post.

How were relays checked?

I would start with a careful cleaning of contacts on the pod, grounds etc.

[1979928]

I'm located in Austin, Texas.

The relays were checked with a meter and seem to be operating properly.

What role does the alternator resisitor play in the charging circuit? I have seen it mentioned numerous times and have seent he part for sale for $3.00. I have always been into replacing any little parts here and there as I found them just to ensure that the car is always in good working order, but have never replaced this part.

The first time the alternator went out I was sitting in a friends driveway at night and one of my headliughts didn't come on all of ther way. They were up, but the passenger side headlight was dimmly lit so I turned the key off and back on quickly and ended up blowing the alternator out. A genious actin on my part.

The car has 98,000 miles on it and has a strong engine mechanically. IT's too bad the electrical is such a pain.

[1979928]

look spaces....

[Danglerb]

Sounds like a pain in the shorts, but with a set of wiring diagrams and a meter any good electrical guy should be able to sort it out. You just may need to become a good electrical guy.

Your 230 miles from Roger in Double Oaks (outside Dallas), but I think there are a few guys in Austin area that might be able to help out, read the diagram while you crawl under the dash, that sort of thing.

Alternators have two wires, big fat wire going off to charge the battery, little bitty wire that wakes up the alternator and gets it excited enough to start making current (generators have magnets inside, alternator don't). On the 928 the exciter wire comes from the battery through the charge warning lamp in the dash and goes to the alternator. Later on Porsche put a resistor in parallel with the lamp since in the old design when the lamp burns out and alternator doesn't charge.

[Alan in AZ]

Sounds like you have many instrument pod issues - did you remove the pod for some reason? if yes - maybe the connections arent correct - I'd suggest you check/clean

Your headlight issue (one side) sounds like a ground problem (or connection problem) to just that headlight. It is not likely what killed the alternator.

Check ther alaternator voltage with a reliable meter - thats the only indication of goodness.

Nothing else on the car can really cause the alternator to generate a sustained too high voltage - its self contained. Assuming the battery is good enough to start the car - its good enough to work properly with the alternator/regulator.

The high/low beam switch is not the same for all years (though its similar). You should not have needed to remove the pod to replace it - but if neither switch works correctly it may actually be the headlight relay that is at fault (its what actually switches the beams). Again not all years use the same relay - check.

Alan