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Alternator Exciter Circuit

 
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2040
Location: MI

PostPosted: Sat Aug 15, 2020 8:28 am    Post subject: Alternator Exciter Circuit Reply with quote

My 931 stopped charging..
I think it might be related to me accidentally shorting the alt power wire on the back of it and/or possibly the exciter wire back there as I was borrowing some 12v from it there and touched something wrong and threw some sparks..

If I turn the key on I dont get any power to the exciter wire..
If I start the car I dont get any power to the exciter wire..
If I jump 12v to the exciter wire on the back of the alternator i can hear it start pulling on the engine..
After jumping power to the exciter wire just for a moment, the exciter wire stays powered up for some reason and alternator keeps working even after removing the jump..
If I shut the car off again I again have no power to the exciter wire, start it and still no exciter power, jump it again and the exciter wire power stays on until I shut the engine off again..
Just a quick jump of the exciter wire and the alt keeps working until shut off again..

No battery light ever.. Donít even know if thats hooked up..

Think I blew something in my exciter wire circuit, but how do I fix/troubleshoot it?
This stuff isnít my forte..
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Paul  



Joined: 02 Nov 2002
Posts: 9451
Location: Southeast Wisconsin

PostPosted: Sat Aug 15, 2020 11:22 am    Post subject: Reply with quote

Are you saying the battery light has never come on when you turn the key to the run position?

Your problem usually occurs when the bulb burns out.

The battery light serves the same purpose as what you are doing manually.

The current flow through the bulb "excites" the alternator to get it going.
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Silver 98 986 3.6l 320 HP "Frank N Stein"
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Paul  



Joined: 02 Nov 2002
Posts: 9451
Location: Southeast Wisconsin

PostPosted: Sat Aug 15, 2020 11:35 am    Post subject: Reply with quote

I just read your camping post, never remove a battery cable with the motor running.

http://www.troubleshooters.com/dont_disconnect_battery.htm
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2040
Location: MI

PostPosted: Sun Aug 16, 2020 12:33 am    Post subject: Reply with quote

Yeah, Iím bad..
So I have to pull my gauge cluster again and check/replace that bulb behind the battery light probably? Ugh..
Should have 12v to the light at all times with the key on?

BTW my oil press regulator seems fine.

Thanks Paul..
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2040
Location: MI

PostPosted: Sun Aug 16, 2020 3:40 am    Post subject: Reply with quote

Have gauges out..

Bulb is fine.. Works..
Have power at both sides of the bulb.. Backside of bulb socket with bulb installed both light up test light..

So the problem must be somewhere between the bulb and the alternator?
Which wire is it coming out of the gauge?

Yes gauge lights/illumination/fuel gauges work..

Have no power at 1 2 4 and 8 out of the back of the gauge, with or without the bulb installed..
So itís a problem in the gauge itself?
Figure one of them should have no power without the bulb, but then get power upon installation of the bulb... But no..

So I figure by the traces it goes to pin 11 but somehow something in my wiring is putting power to pin 11 when it gets plugged into the board, even when it is just the bare board..

11 doesnt short to anything on the board, but something in the harness is putting power to pin 11 only when the bare board is plugged in..

I hate this crap, Im so confused..
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Last edited by Fasteddie313 on Sun Aug 16, 2020 5:04 am; edited 1 time in total
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Paul  



Joined: 02 Nov 2002
Posts: 9451
Location: Southeast Wisconsin

PostPosted: Sun Aug 16, 2020 4:30 am    Post subject: Reply with quote

do you have continuity from the bulb socket to the alternator?
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2040
Location: MI

PostPosted: Sun Aug 16, 2020 5:06 am    Post subject: Reply with quote

Paul wrote:
do you have continuity from the bulb socket to the alternator?


I guess not.. Since I have power on both sides of the bulb but not the wire on the alt..
Darn cheap multimeter got rained on a bit and quit so Iím only working with a test light..

Thinking pin 11 to the alternator wire failed and is now shorting to something else in the harness somewhere.. But only on the gauge side..

Checked the whole gauge board.. No shorts on the gauge board itself..
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2040
Location: MI

PostPosted: Sun Aug 16, 2020 8:00 am    Post subject: Reply with quote

Main culprit turned out to be the amp connector where the blue alt exciter wire goes through with the starter wires... Was full of crap and the blue wire pin coming out of it..

Other than that, wiggling lots of stuff, and the small short to positive somewhere in it.. Who knows, but it charges again now and is basically back to normal..

Man I hate pulling the gauge cluster.. Getting it all back in sucks a lot..
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Paul  



Joined: 02 Nov 2002
Posts: 9451
Location: Southeast Wisconsin

PostPosted: Sun Aug 16, 2020 8:15 am    Post subject: Reply with quote

Glad to hear, I just spent the last 15 minutes pouring over wiring diagrams trying to help you find all the connectors on that circuit. I really enjoy this kind of stuff, I'm not kidding it's fun.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2040
Location: MI

PostPosted: Sun Aug 16, 2020 11:03 am    Post subject: Reply with quote

Anything on it between the gauge and the amp connector that could leak some positive juice into it?
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