Sharks

I pulled the engine in my wife’s 1983 911 SC about a month ago to fix oil leaks at the back of the engine. Everything went well, but when I started the car the battery charge light on the dash came on. I figured the battery was just week and it would eventually go out after driving for a while, but it didn’t. I purchased a new battery as I didn't know how old the battery was as it came with the car. No luck, light is still on.

Low voltage light does not come on with key on, but comes on after start and stays on while running. Light goes off at key off.

Done So Far:
New battery voltage and cigarette lighter voltage 12.3 V
Cleaned ground strap and added second strap from body to trans
Cleaned ground strap and terminals next to battery
Cleaned 14 pin connector in engine compartment on driver side
Pulled alternator and checked connections (Red - 10mm nut bottom, Brown - 8mm nut bottom, Blue - 8mm nut top – Picture below)
Pulled voltage regulator, cleaned shaft and checked brushes
Attached red, brown, and blue wires to back of alternator so I could run the engine and take the following readings

Running with Low Voltage Light On
Red to Brown = 135 mV
Blue to Brown = 1.7 V

If I rotate the key to the off position briefly while the engine is running, then back to on, the light on the dash goes off and stays off after the engine stumbles, then continues to run and I get the following readings

Running with Low Voltage Light Off
Red to Brown = 0 mV
Blue to Brown = 11.7 V

---> No power to alternator with key on or off <---

I’m trying to figure out if this is a coincidence that this low voltage light came on after the engine install (never had a problem before engine removal), if the voltage regulator is bad, or if the alternator is bad. Any suggestions/help appreciated thanks.

theiceman

so i dont suppose you took it in to have bench tested for free while you had it out ?

Sharks

I haven't been able to find a local shop that can test it. Their test equipment is setup for certain model years and this alternator is 31 years old. I suspect the alternator is bad, but it baffles me that I am not seeing voltage at the hot wire going to the battery.

wwest

D+ wire is shorted to ground.

My "guess".

Sharks

Got the alternator checked at lunch today and it's good. Will look after work today, but I think I may have missed connecting a wire at the starter when I installed the engine. Is there a wire that runs from the starter to the alternator. If so, it's probably trapped between the engine and the body, and that would explain why I don't have any voltage at the alternator.

Sharks

As I thought, when I installed the engine I trapped the wire that leads from the starter to the alternator. When I got home last night I found the wire, installed everything and all everything is working again.

Thanks for your help guys.

Mark