1980 911 SC Electrical Issue

[356sccoupe]

I had my car out for a drive this morning. After about an hour, the tach started flopping around and after a few minutes quit entirely. Then the odometer stopped working, but the speedometer was Ok. Then the turn signals weren't working, at least the light wasn't flashing on the instrument panel.

After I got home I let it sit for about an hour and then went to see what else wasn't working. Now everything is working so I'm guessing a loose wire??

Where should I start looking?

[timmy2]

Start with checking the battery terminals are tight. Then move on to checking/cleaning fuses, followed by engine ground strap and body grounds.
Check your alternator voltage output. At idle and while driving.
Lots of posts on how to check all of these items.

[356sccoupe]

Thanks!

[RDM]

Well, there's nothing electrical about the odometer, so there may be more than one problem. I'd look at grounds. The main ones are battery to body in the trunk and body to transmission underneath by the passenger rear wheel. After that there are several other grounding points that could be a source of your problem.

But Dennis is the expert, so believe him first!

[timmy2]

Agree odometer is a separate issue.
Lots of Intelligent people know about electrical problems on these cars.
Dru is one of them...

[GAJon]

Originally Posted by 356sccoupe

I had my car out for a drive this morning. After about an hour, the tach started flopping around and after a few minutes quit entirely. Then the odometer stopped working, but the speedometer was Ok. Then the turn signals weren't working, at least the light wasn't flashing on the instrument panel.

After I got home I let it sit for about an hour and then went to see what else wasn't working. Now everything is working so I'm guessing a loose wire??

Where should I start looking?

Might pull the tach and speedo and do some checks. I shorted some stuff out on the dash through my own carelessness and it caused somewhat similar symptoms minus the odometer issue you're seeing.

See if any wires are shorted to ground as a start. There should be a brown wire that is spliced in several places behind the gauges.

[Walt Fricke]

Nothing electrical about the odometer? After the change from cable speedometers/odometers, the odo is some kind of solenoid which fires after X pulses from the speedometer sensor in the transmission. I believe he is concerned with his SC, not his 356.

I'd check the battery. If, perchance, the voltage regulator has quit working, its voltage will keep dropping. When that happened to our 3.2 (at night, of course), letting the car (which quit) sit a while allowed a few more miles of driving - it seemed the battery could somehow do a bit better after a rest - though a flatbed was still needed. But some systems may be more sensitive to voltage levels than others. I think the tach is one.

But it could just be a bad ground - more resistance as it heats up - or loose connection which expands a bit with heat.

[356sccoupe]

Dennis, your diagnosis was correct.

New alternator solved the problem.

Thanks for your help and knowledge!