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Old 08-25-2009, 08:30 AM   #1
mikew
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Default GM 10Si alternator wiring issues

To start off,yes I did search and couldn't find an answer to the problem I'm having. I read all of the posts and found the proper wiring diagrams for a 3 wire 10si.

I installed a new alternator (3 wire internal regulator) in my '62 comet. I wired the main lug on the alternator directly to the battery cable side of the ford starter solenoid. I jumped post 2 from the 2 post connector to the main lug on the alternator. I've tried connecting the 3rd wire (post 1 on the alternator) to 1.) load side of the ignition switch 2.) The ignition post of the starter solenoid and 3.) the main lug on the alternator. All of these produced no change.

This is what's happening.... I'm only getting 12.5 volts as shown on my new voltmeter and confirmed with my multimeter. Once in awhile, it will register around 14 volts, but if I shut it off and restart it shows 12.5 again.

If I disconnect everything from the alternator, I read about 18 volts at the main lug on the alternator. Because of this, it seems that I have a voltage sensing problem.

Any of this make sense? What am I missing? Or is the regulator bad in my new alternator?

Thanks in advance
Mike
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Old 08-25-2009, 08:38 AM   #2
d2_willys
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Default Re: GM 10Si alternator wiring issues

1) Wire from #2 terminal should go to the battery + or to the battery + side of the starter solenoid. This will sense the voltage at the battery, not at the alternator output.
2) Wire from #1 should go to a diode (striped or cathode end) or idiot lamp then the other side of lamp or diode to ignition terminal of ignition switch. By doing this it will prevent run-on when ignition switch is shut off.

The other two terminals you mentioned are NOT what to do.

3) You may want to check your main lug wire to starter solenoid. This sounds like an intermittent connection. Remember to make this at least #12 gauge stranded wire.

Hope this helps
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Old 08-25-2009, 08:40 AM   #3
55chieftain
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Default Re: GM 10Si alternator wiring issues

The 3rd wire should be hooked up to a gauge or light to make the alt work. The 2 pin connector with red/white wires, the red to the pos post on alt and the white wire is the 3rd wire , sounds the the rest is wired ok.

d2 types faster than I do, def need the diode.
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Old 08-25-2009, 09:00 AM   #4
mikew
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Default Re: GM 10Si alternator wiring issues

So if I understand right, the third wire (post 1) should feed the voltmeter and everything should be ok? I will add a diode if it runs on, but I want to get it operating and charging properly first. Also, that's the first time that I've heard that the wire from post 2 should go to the battery and not hook to the main alternator lug. I'll try that.

any other input?
thanks

Last edited by mikew; 08-25-2009 at 09:01 AM. Reason: grammar
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Old 08-25-2009, 09:20 AM   #5
patrick2965
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Default Re: GM 10Si alternator wiring issues

May I throw in a question?
If you have the alt main lug wire going to the bat cable starter terminal on a Chevy application, would lug #2 to the main lug also be correct?
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Old 08-25-2009, 09:20 AM   #6
d2_willys
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Default Re: GM 10Si alternator wiring issues

Quote:
Originally Posted by mikew View Post
So if I understand right, the third wire (post 1) should feed the voltmeter and everything should be ok? I will add a diode if it runs on, but I want to get it operating and charging properly first. Also, that's the first time that I've heard that the wire from post 2 should go to the battery and not hook to the main alternator lug. I'll try that.

any other input?
thanks
Post #1 wire should either go to a diode or to an idiot lamp, not a voltmeter. If you have a voltmeter gauge this should be hooked to the ignition switch IGNITION terminal (with other terminal to ground). This would be the same terminal as the idiot light and Anode side of diode would go to.
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Old 08-25-2009, 09:29 AM   #7
mikew
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Default Re: GM 10Si alternator wiring issues

What is the right model or rating of diode to get at radioshack?
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Old 08-25-2009, 09:37 AM   #8
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Default Re: GM 10Si alternator wiring issues

Sounds like a bad regulator to me
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Old 08-25-2009, 10:14 AM   #9
mikew
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Default Re: GM 10Si alternator wiring issues

Thanks for the delcoRemy link, I'll check that out.

I read somewhere else last night that I can connect both wires (1 and 2) to the main lug and connect that to the battery, and it will act like a 1 wire alternator. Is this BS? I tried it last night and nothing happened.
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Old 08-25-2009, 07:28 PM   #10
d2_willys
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Default Re: GM 10Si alternator wiring issues

Quote:
Originally Posted by mikew View Post
Thanks for the delcoRemy link, I'll check that out.

I read somewhere else last night that I can connect both wires (1 and 2) to the main lug and connect that to the battery, and it will act like a 1 wire alternator. Is this BS? I tried it last night and nothing happened.
I believe this is true, but you have to remember that the alternator needs "exciting" for it to start to output. In most cases you have to rev the engine up to 1500 rpm for the one wire alternator to start charging.
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Old 08-26-2009, 06:12 AM   #11
Tugmaster
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Default Re: GM 10Si alternator wiring issues

This site has some excellent info on SI alternators.

http://www.madelectrical.com/
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Old 04-15-2013, 02:57 PM   #12
hoop98
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Default Re: GM 10Si alternator wiring issues

The Red sense voltage is how the regulator senses voltage.

In a 1 wire it goes to the batt terminal.

In a 3 wire it can compensate for voltage drop in the charging wire.

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Old 04-15-2013, 03:01 PM   #13
rust
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Talking Re: GM 10Si alternator wiring issues

whats an alternator?
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