electrical problems

[beany]

I'm having some electrical problems with my 1980 sc. I had a iinterior light wire short out and burn up which I have fixed. Since that time I have been having electrical gremlins. First off, after starting the engine and idling it at 900 rpm the tach with go over to 4000 rpm while the engine does not increase in speed. Pulling the headlight switch on will return it to 900. Lately I have been having additional problems with my headlights. they are on low beams and the dash highbeam
light is lite up. Any help would be greatly appreciated. When I drive the car down the road the tach will register all kinds of strange readings, 4000, 3000, and then go back to 0 rpm... Thanks.

[Tigerrat]

A good place to start is your charging voltage. Should be around 14. If you see 15v+ strange things can happen. Likley problem is voltage regulator.

[otto in norway]

I think maybe this is a case of burning more wires than you thought...
As you may know, many cables cross other in the wiring loom.... (Is that the right spelling?)

So, if one wire burns, you may have others connecting where they shouldn't...

Good luck to ya!

[gamatt]

Beany,



I agree with the statements above and offer the following...if the charging system is off the hook you should see other obvious faults. Your lights should be much brighter than usual, inside and out and when things get to the 15+ to 16 volt range you start to see equipment failures. (burnt out lights, etc.)



Otto is on to something, although there may be a slightly different read on how things happened. Your car is 29 years old. And although I love my Porsche too, the wiring in the car sucks when compared to a modern automobile. Lots of exposed wires and connections running throughout. The fact that your interior light flamed-out and the other issues happening at the same time may or may not be related. Don't assume, just start with the basics and work through to a solution. Try to work each of your problems as a separte issue. I've gone through the wiring diagram for your 1980 and the problems you describe don't seem to be naturally linked. Although as Otto pointed out, they could be unnaturally linked due to an intermittant short caused by the original wire melt...



First, go ahead and verify your system voltage with the car running. It should hang nice and steady at between 13-14.5 volts. If that's good, then the tach needs three things to work. Power, ground and in your case, an electrical signal from the Electronic Ignition Control Unit. Pull the Tach out of the dash and verify it has a good connection for both the power wire (red wire w/black tracer) and the brown ground. Then turn on the key and check the power supply wire for system voltage. Losing either of these will cause the Tach to wobble while driving. Next test the EICU wire (black w/ violet tracer) to make sure it is'nt shorted out or broken and that its connections at both ends are good. This can be done by disconnecting it at both ends and testing the wire from one end to ground and to the hot side (B+) of the car. There should be NO connection to either with the wire disconnected at both ends!...make sure the battery is disconnected when you do the test our you'll blow your meter to little pieces when you do the hot side test. Finally, check the feed wire to make sure its good end to end, physically and electrically. If it all looks good, then you're down to either a bad Tach or a bad feed from the EICU. The best way to check these two items is to swap them out if you can.



As for the headlights, according to my wiring diagram for the 1980 model, the only way you could get the symptom you describe, high beam indicator in the Tach on and the hign beams not working is:

1. Both high beam lights burnt out and this would take me back to "is the system voltage OK?"

2. Broken/missing/ bad connection from the wire to the high beams.



Essentially the logic here is the wire that powers your indicator light comes out after the fuse that supplies power to the left high beam. Given what you've said, the high beam switch is working because the indicator light comes on a stays on. I know it's counter intuitive, but check both high beam lights. You can do this by shorting a 12 volt lead to the high beam light. It will spark so make sure you're in a well ventilated area before you try this one!



Last, most of our cars a susecptable to vermin...not gremlins. If you store you car for long periods you may have mice and they love wiring insulation. Even if you use your car daily check you wiring for signs of attack. We just had our 2002 Mitsubishi daily driver serviced and the local Jiffy Lube removed a football sized mouse house out from under the air filter housing.



Write back if you need more help. Good Luck...chasing wiring problems sucks. And remember to disconnect all power before you do any resistance checks!!!!!!



Gordon

[Gunter]

beany:
Good advise re: checking your charging Voltage. Tach jumping is usually connected with regulator failure.
Re: burned wire for interior light:
The fuse for interior light and glove box is also used by the Frequency Valve (FV) in your CIS; very essential that the fuse is good and the FV has power.

[gamatt]

Did you ever get your car fixed?

G

[vascott01]

also make sure that you have the grounding straps grounded....