Charging problem 911S 1976

[JKR001]

Hi Everyone

I'm having a charging problem with my 911S 1976 2.7L

Alternator light doesn't light up before start so replaced bulb (aware of the need to have a working bulb to excite alternator) - still doesn't light up.

Battery measures 11.9V before start and 11.2V after start up.

Car dies as soon as battery fails.

If the alternator has failed, then wouldn't the light still light up before start up?

Any ideas on what I should do?

Thanks

[clarkd]

If you have known good bulbs and clean connections then one possibility is a worn brush not making contact with a slip ring on the alt rotor shaft.

[Targalid]

I can tell you what I recently did with my intermittent charging system. It may help you. My alternator bulb did not light consistently but I could get it to light intermittently by having my assistant in the driver seat watch the instruments while I moved wires in the engine compartment fuse box area. When wires at the 14 pin connector and/or the voltage regulator were moved, the alternator bulb would light. Further investigation led to replacement of a cracked 14 pin connector housing. This made the alternator bulb light more consistently. I thought I had the problem solved but I still had intermittent low voltage. Further checking led me to the noise suppressor. On my 76, the blue wire from the 14 pin connector which carries current to the alternator bulb and to the alternator exciter, is routed through the noise suppressor before going to the voltage regulator. These two parts are next to each other in the fuse box/CDI area of the engine compartment. I disconnected the noise suppressor, plugging the three prong connector directly into the voltage regulator and voila, battery charging is now consistent. The only problem is the noisy radio signal. I may reinstall the noise suppressor after thoroughly cleaning the connectors. I hope this story helps you find your problem. Good luck.

[JKR001]

Thanks - will check connections and report back

[supdaf]

I second the suppressor. Exact same issue with my 76. Removed same, lasts long time.

May not help but something to check.

[JKR001]

Pulled out alternator and had it tested. Turn out to be a problem with the rotor which was a simple fix. Alt light now works and normal charging has returned.