I got 99 electrical problems, but my mechanic only finds one
 

Hi

I’m new to this board and to 911’s.

Last year I bought a 911 2.7 coupe from 1976. The clutch and gear box had a few problems – unfortunately not the ones that are cheap and easy to fix. Anyway, that’s behind me now and I’m almost as happy as my newly rich mechanic.

BUT the car also has electrical issues, which unfortunately are hard to pinpoint. The previous owner had left a gazillion new and used fuses in the glove compartment, which should have tipped me off.

Twice I’ve had a battery that was totally flat after the car had been sitting for a week or so. After a quick drive, and yet another week’s pause, there was no problem at all.

Couple of weeks ago I took the car for a night drive. The alternator light came on as it usually does for the first few miles. But this time it stayed on.

After visiting with some family for some hours I wanted to drive back. But once again the battery was flat. So we push started it. But as I drove along the engine kept shutting out and after a few miles I had to stop at the road side and call for help.

So now the car’s back at my mechanic. According to him I simply need a new alternator to get going again, which is fine by me. But I’m concerned that it’s only the tip of the iceberg, since a faulty alternator shouldn’t lead to a battery discharge. Or?

Rgds,

Holger

A bad altenator will not charge the battery.

If it is original, it may be time for a new one, not a rebuild.

After that, a prolonged session with a multimeter and the car's original wiring diagram will solve everything.
Clean the earths!

Yep, if your alternator isn't working, the electrical power the car needs will come from the battery until it dies.

Yes, check the major ground connections first. "ground" or "earth" depending on your location :D Engine ground strap connects the engine/transmission to the cars under-body. Hard to get to without jack stand or a lift. Remember, the engine is supported by four rubber isolation pads. The ground strap is required for electrical continuity.

Then ground between the battery and the chassis in front. If they have any green corrosion on them, they are in bad shape.

Then start looking/checking the wires to see if you have corrosion (green patina) or oxidation. Look for loose wires at the fuse block. look for places where the wire might be rubbing the chassis. Maybe there is a short from the insulation wearing through.

It could be a easy as finding some wires are a little corroded, and a simple scrub with steel wool or fine Emory cloth is enough to expose fresh copper.

also dont be surprised if your mechanic wants to sell you a new battery . This is not unusual and not a bad idea if you have had a slowly dieing alternator that cant charge the battery . Usually both are done by the end.

it is not unusual to have a bad diode in your diode pack in your alternator that will bleed down your battery, so if thats the case the alternator will fix that .

BTW i am NOT Tom Jones . .it just apears that way .. :)

Right, thanks for the replies and suggestions. I had no idea that the alternator could bleed down the battery, so yeah, hopefully that'll fix everything.

Obviously I'll keep the old alternator and try to give it a restoration job myself. Should be fun I suspect. :)

Rgds,

Holger

Friends want to make sure you circuits closed
Solve one problem at a time but I highly recommend having a reliable power source to start with.

You probably have a remote voltage regulator on your year of car. Make sure your mechanic knows this as it is under $50 to replace it.
Cheap insurance to have a spare one too.