81 Wiring Alternator Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

AlbertaClassic · 06-02-2017, 12:10 PM

Hello, I am new to this part of the forum. I recently purchased my first squarebody, an 81 GMC K2500. Due to a recent sale of my DD, I am in a hurry to get this thing running consistently. I have killed a battery or 2 (I'm not very mechanically inclined, but learning) and have done the voltage tests on the battery and have confirmed the battery isn't getting any charge. Atleast up to 2500 RPMs. So I need a quick fix to get the alternator running. It looks like to me that the battery charge post (?) on the alternator isn't connected to anything. See attached photo below. There is a loose red wire just hanging there. In theory if I hook that back up it should work correctly, no? Or, for now would it be possible to run a 10-12 gauge wire from the battery post straight to the alternator? Should I fuse it? I apologize if this should be in electrical, I'm just hoping to get it sorted out. Thanks in advance.
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**mongocanfly** · 06-02-2017, 01:53 PM

There supposed to be a wire with a ring terminal on the stud on the back of the alternator

**mongocanfly** · 06-02-2017, 02:26 PM

Like this..its a heavy wire about 10ga or so..

AlbertaClassic · 06-02-2017, 04:09 PM

Okay. So I have a wire that's there, theoretically if I hook it up I should be good to go? If the harness is a little butchered, what would be the best way to go about hooking it up to the battery? Would a direct line work? Thanks
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**mongocanfly** · 06-02-2017, 07:08 PM

My alternator wire goes to the 2 pole junction block at the center of the firewall above the distributor

Dead Parrot · 06-02-2017, 07:30 PM

If you are talking about that red wire in your first pic with all the tape on it, probably yes. The other end of that wire should run to the junction point on your firewall. Same place as the red wire in the two wire connector on the alt.

Disconnect the battery when you test your hookup since IF that red wire is the wire that is supposed to be connected to the alt, it is full hot even if the ignition is off.

AlbertaClassic · 06-03-2017, 10:27 PM

The wire that was there was through the junction to the battery. Everything is good to go and I'm at 14.5 amps at idle now. Thanks for all your help
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AlbertaClassic · 06-03-2017, 10:30 PM

Volts*
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06-02-2017, 12:10 PM	#1
AlbertaClassic Registered User Join Date: Nov 2015 Location: Taber Alberta Posts: 400	81 Wiring Alternator Help Hello, I am new to this part of the forum. I recently purchased my first squarebody, an 81 GMC K2500. Due to a recent sale of my DD, I am in a hurry to get this thing running consistently. I have killed a battery or 2 (I'm not very mechanically inclined, but learning) and have done the voltage tests on the battery and have confirmed the battery isn't getting any charge. Atleast up to 2500 RPMs. So I need a quick fix to get the alternator running. It looks like to me that the battery charge post (?) on the alternator isn't connected to anything. See attached photo below. There is a loose red wire just hanging there. In theory if I hook that back up it should work correctly, no? Or, for now would it be possible to run a 10-12 gauge wire from the battery post straight to the alternator? Should I fuse it? I apologize if this should be in electrical, I'm just hoping to get it sorted out. Thanks in advance. Posted via Mobile Device Attached Images

06-02-2017, 01:53 PM	#2
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: 81 Wiring Alternator Help There supposed to be a wire with a ring terminal on the stud on the back of the alternator

06-02-2017, 02:26 PM	#3
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: 81 Wiring Alternator Help Like this..its a heavy wire about 10ga or so.. Attached Images

06-02-2017, 04:09 PM	#4
AlbertaClassic Registered User Join Date: Nov 2015 Location: Taber Alberta Posts: 400	Re: 81 Wiring Alternator Help Okay. So I have a wire that's there, theoretically if I hook it up I should be good to go? If the harness is a little butchered, what would be the best way to go about hooking it up to the battery? Would a direct line work? Thanks Posted via Mobile Device

06-02-2017, 07:08 PM	#5
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,671	Re: 81 Wiring Alternator Help My alternator wire goes to the 2 pole junction block at the center of the firewall above the distributor

06-02-2017, 07:30 PM	#6
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,611	Re: 81 Wiring Alternator Help If you are talking about that red wire in your first pic with all the tape on it, probably yes. The other end of that wire should run to the junction point on your firewall. Same place as the red wire in the two wire connector on the alt. Disconnect the battery when you test your hookup since IF that red wire is the wire that is supposed to be connected to the alt, it is full hot even if the ignition is off.

06-03-2017, 10:27 PM	#7
AlbertaClassic Registered User Join Date: Nov 2015 Location: Taber Alberta Posts: 400	The wire that was there was through the junction to the battery. Everything is good to go and I'm at 14.5 amps at idle now. Thanks for all your help Posted via Mobile Device

06-03-2017, 10:30 PM	#8
AlbertaClassic Registered User Join Date: Nov 2015 Location: Taber Alberta Posts: 400	Re: 81 Wiring Alternator Help Volts* Posted via Mobile Device



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