Jumping tach, G light flashing and smoke through the defrost...

[Coach House 911]

After a summer of driving my '79 SC with no issues, all the while having the G- dash light flutering bright to dull on and the tach jumping eratically, last week small puffs of smoke rose from the left defrost. It was hardly noticable however soon after driving the smell of burning rubber became obvious.
I then drove home and garaged it and have not started it since.

Does anyone know if it is the alternator or possibly the regulator and a way to determine which?

Thanks,
Mike

[Grady Clay]

(I deleted my reply on the Engine Forum and repeat here.)

Mike,

STOP
DISCONNECT THE BATTERY

You need to look behind the dash and see if you can spot any damaged wires.
Have a fire extinguisher handy.
Don’t leave the car unattended with the battery connected.

(You can delete the original post to avoid duplication.)

Best,
Grady

[wwest]

Originally Posted by Coach House 911

After a summer of driving my '79 SC with no issues, all the while having the G- dash light flutering bright to dull on and the tach jumping eratically, last week small puffs of smoke rose from the left defrost. It was hardly noticable however soon after driving the smell of burning rubber became obvious.
I then drove home and garaged it and have not started it since.

Does anyone know if it is the alternator or possibly the regulator and a way to determine which?

Thanks,
Mike

Your alternator stator winding is shorting out internally, intermittently shorting out. Worse on bumps, bumpy roads...?

[Coach House 911]

Bumpy roads don't seem to have an effect. The tach will jump even at idle. when I blip the throttle just a tiny bit the tach jumps way more than it should and bounces beyond the actual rpm's. When it got really bad the parking brake light also elluminated full red even though it was not applied whatsoever.
The smoke started only a minute or so while on cold warm up.
A Porsche tech told me today that it is most likley my alternator being shot.
Would it not be my regulator?

[longhornchris04]

I had a similar problem, sans the smoke smell.

In my case I had a (poorly installed) alarm wire (P.O.) that had rubbed off its insulation and was causing a ground fault. A little electrical tape, some re-routing (plenty of slack), and some tacking down and I haven't had a problem since.

I doubt yours is as simple, but check for electrical faults. Anything that grounds against the chassis could be causing an issue. Baring that, your alternator or regulator may be going.