993 Alternator issue

[almico]

I just replaced my fan/bearing and while it was out, had the alternator rebuilt. The car has 110k miles so I thought it prudent. It was working fine before the job.

I got it all back together this morning and the alternator is not charging. I talked to the shop that did the rebuild and he said it was pushing 14.3V on his bench. His first guess was to check if the exciter lead is getting 12V from the battery when the the car is keyed on. Easier said that done since I have to pull the whole A/C, fan, housing out to check. Any chance the exciter wire is fused? If so, where? Can I check for 12V to this wire on the other end?

[almico]

I found the electrical diagram in the service manual and it seems the exciter wire gets its voltage off the positive terminal on the starter. The starter works, so it is not a fuse issue. I'll tear it down again tonight and see what I see. It's a bear getting the cover back on the back of the alternator so I likely boogered something up.

[almico]

Everything is apart again.

I need to confirm that the exciter wire is supplying 12v to activate the alternator. The exciter wire and big charging wire are conjoined inside a big terminal lug. I hate to cut it apart to test the exciter independently. The wiring diagram says power to the exciter comes off the fuse block. Where??? Bentley book no help.

Does anyone know where the other end of the exciter wire connects to the fuse block? Fuse, relay?



This is what I found in Bentley:

[almico]

I found this on a Rennlist thread.

https://rennlist.com/forums/993-forum/1163212-charging-problem.html

[Clay Perrine]

Don't cut it apart. You have the wrong wire. The alternator "exciter" wire is the one connected to the charge light in the dash. B+ is the battery voltage wire, I.E. the charge voltage going back to the battery. D+ is the field "exciter" power. When it gets power it energizes the field windings to make it charge.

Check the ground wire connected on the back of the alternator, and make sure your generator light comes on when you turn the key on before starting the car.

[almico]

Originally Posted by Clay Perrine

Don't cut it apart. You have the wrong wire.

Bingo! I assumed the exciter had to be a switched lead, but I didn't read any voltage when the car was keyed on.

To compound the issue I was dang sure I "copied" the wiring correctly. Shoot, it's only 3 wires and one of them is thick as a battery cable. I had the exciter to ground on the alternator. Glad it's working, sad I'm capable of the stupidest of mistakes.

Now it's time to take on the front shocks. What could possibly go wrong?!

[LM964]

Originally Posted by Clay Perrine

Don't cut it apart. You have the wrong wire. The alternator "exciter" wire is the one connected to the charge light in the dash. B+ is the battery voltage wire, I.E. the charge voltage going back to the battery. D+ is the field "exciter" power. When it gets power it energizes the field windings to make it charge.

Check the ground wire connected on the back of the alternator, and make sure your generator light comes on when you turn the key on before starting the car.

Indeed. Like mine, if the clock gauge charging lamp is blown then no circuit 'excite' - always good to check for that first. Otherwise it's a case of 'blipping' the throttle >3k rpm to 'wake up' the charge circuit each time. I fitted a separate digital volt display under the dash making sure I know all is good. Glad you're all sorted now.

[Clay Perrine]

Originally Posted by LM964

Indeed. Like mine, if the clock gauge charging lamp is blown then no circuit 'excite' - always good to check for that first. Otherwise it's a case of 'blipping' the throttle >3k rpm to 'wake up' the charge circuit each time. I fitted a separate digital volt display under the dash making sure I know all is good. Glad you're all sorted now.

Same here. I have the Clewett serpentine belt conversion on my 964 powered 914, and when you first start the car, the generator light stays on and the volt meter reads 12v until you blip the throttle. Then the light goes out and the voltmeter comes up to 14v.

[LM964]

A 3.6 flat six 914... now there's a thought. Most excellent!