1971 911T Alternator Re-install problem

[tcj911t]

I had my 1971 911T Bosch 55 amp alternator repaired at a local shop. It only needed new brushes. I re-assembled everything and now get no generator light on my dash when ignition key is turned on? I am hesitant to try to start engine without generator light acting normal. Before repair my generator light was working fine and was bright when ignition key on and then stayed dim when engine running. Voltmeter showed no charge.

Any ideas what is wrong? I am not excited about tearing everything apart again, ugh. Repair shop claimed alternator tested good once new brushes installed and bearings were good. I double checked that all wires were connected correctly on alternator during reinstall. One question I have is how to reattach ground strap to alternator bolts before or after fiberglass shroud is fitted over alternator bolts? Thanks for any help!

[jason2guy]

you have a wire out of place. pull it back out and connect the ground strap directly to the alt. that shroud is a pain in the ass. ive modified mine so only 2 bolts hold on the shroud, and the rest are directly against the back of the housing

[tcj911t]

Can the ground strap connected outside of the fiberglass shroud cause my symptoms or is there another wire out of place?

Attached are some pictures I took as I removed the original alternator. I made sure the red wire went to the B+ terminal (on the left looking from above facing the engine) and the blue wire on the smaller terminal below the other B+ terminal. And the black wire/plug in the only connector for it. Since I had the fan out, I also included a picture of my fan cleaned up with Gibbs oil.

I also am using a new Behr solid state regulator that I purchased to replace my original larger one. I purchased the new regulator when I first was troubleshooting my charging problem. Both have same plug on bottom but new regulator is slightly smaller but fits in the installation. The alternator shop tested both regulators and recommended I use the new solid state one. I plan on trying the old regulator to see if there is some incompatibility with the wiring on my 911. I am not sure the new regulator behaves the same regarding the generator light on my dash?

[tcj911t]

My alternator is still not working? I took everything apart and made sure the ground strap from the engine connected directly to the metal fan outer enclosure holding the alternator and not insulated by the fiberglass. I reinstalled my original VR and now I get a slightly dim and flickering light with the ignition on that remains on and dim when I start the engine, but still no charge? This is exactly the symptoms I started with. My guesses on what the problems could be are:

1. The alternator shop that did my repair did not do it correctly?
2. Both my original VR and my new VR are bad?
3. I have another wiring problem in my car that is causing my symptoms?


I have spent quite a bit of time and effort so far un-installing and re-installing the alternator and VRs and am pretty stumped on what the problem is? Assuming the alternator is good as tested by the repair shop, what other things can I test to troubleshoot the problem?

[timmy2]

check ground strap from trains/engine to body is good.
Try another VR.
Ask shop if the commutator rings were good and if they seated the new brushes.

[Targalid]

Why did you have the alternator repaired? That is, what symptoms caused you to think it needed repair?

[tcj911t]

I think I got it! I removed the original VR and replaced it with my new solid state Behr VR. I also noticed that there was some sort of noise filter between the alternator and the VR so I removed it and voila it works. I get a bright red light with the key in the ingition and then the light goes out and I see charging voltage on my cigarette lighter voltage meter. My thoughts are that I shouldn't need the noise filter with the new solid state VR. I am not 100% sure if removing the noise filter fixed it or improving the ground strap contact to the alternator fixed it? Before I improved the ground strap connection, I got no light at all with the new VR installed? I added some pics of the new and old VRs and the noise filter I removed.

My original symptoms were a dim and flickry generator light that would occasionally go out after a mile or so of driving. Recently it quit all together and I never saw a charging voltage on my meter. The alternator repair guy said my brushes were shot but my bearings and everything else looked good. He also tested both my original and new VR and said both worked, but to use the new solid state one if possible.

Thanks for the help. It was more work than I thought, but now I feel more comfortable removing the fan and alternator if I ever need to again.