Ain't This Wire Supposed To Be Hooked Up? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BRL · 07-16-2018, 02:39 AM

LONG ago, I extended my 6 cylinder alternator wiring from the drivers side to the passenger side for a V-8.

At the same time I went with an internally regulated alt. setup.

Problem is I think the heater hose has broken one of the wires off from the plug, but it has been so long since I did this work that I'm not sure if it was ever connected.

Seems to charge OK according to the volt meter.

Just don't want to connect it and then have the truck explode!

Did it break off you think?

bill3rail · 07-16-2018, 08:12 AM

If it works don't fix it!

If you are that curious, trace the wire to see where it comes from.

**VetteVet** · 07-16-2018, 02:40 PM

I would speculate that it is the alternator exciter wire that turns on the alternator when you turn the key switch to ignition. Measure it for 12 volts with the key on and zero with the key off.

Depending on how the conversion alternator was wired, it will be in the old external regulator harness and will lead back to the firewall connector. If it is the wire I think it is then it should be a 16 gauge brown wire at the connector.

The reason the alternator still charges, is that the fields in the alternator are magnetized from the current this wire carries, along with the other red wire in the alternator plug. The fields retain this magnetism when the truck is not running for a period of time until it bleeds off, and then they will have to be recharged. It's called residual magnetism and is similar to what happens when a screwdriver is held with a magnet for a short period of time. If the truck sits for a couple of weeks it may not charge when it is started.

On the cab side of the firewall this brown wire becomes a 20 gauge yellow or brown, with white stripe resistance wire, and it is connected to the accessory terminal on the key switch.

This wire feeds the internal regulator and tells it how much current to let the red wire feed the alternator fields which controls the alternator output. I'm surprised that you haven't overcharged or undercharged the battery. From your picture it appears that the wire just broke away from the no. 1 terminal on the alternator.

BRL · 07-16-2018, 03:44 PM

Thank you for your help VetteVet!

I probably just picked up the plug at a salvage yard and didn't color code anything.

I just wrapped up some extended wires with tape and plugged it in.

I will shorten the heater hose to provide clearance away from that plug and either fix or replace the plug itself.

Again much thanks for the reply.

07-16-2018, 02:39 AM	#1
BRL Registered User Join Date: Jun 2014 Location: Tahuya WA Posts: 510	Ain't This Wire Supposed To Be Hooked Up? LONG ago, I extended my 6 cylinder alternator wiring from the drivers side to the passenger side for a V-8. At the same time I went with an internally regulated alt. setup. Problem is I think the heater hose has broken one of the wires off from the plug, but it has been so long since I did this work that I'm not sure if it was ever connected. Seems to charge OK according to the volt meter. Just don't want to connect it and then have the truck explode! Did it break off you think?

07-16-2018, 08:12 AM	#2
bill3rail Registered User Join Date: Jul 2013 Location: LI, NY 11801 Posts: 1,140	Re: Ain't This Wire Supposed To Be Hooked Up? If it works don't fix it! If you are that curious, trace the wire to see where it comes from. __________________ 1970 C10 8' Fleetside, L6 250, 3 on the Tree. The most basic of pickup trucks!

07-16-2018, 02:40 PM	#3
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,703	Re: Ain't This Wire Supposed To Be Hooked Up? I would speculate that it is the alternator exciter wire that turns on the alternator when you turn the key switch to ignition. Measure it for 12 volts with the key on and zero with the key off. Depending on how the conversion alternator was wired, it will be in the old external regulator harness and will lead back to the firewall connector. If it is the wire I think it is then it should be a 16 gauge brown wire at the connector. The reason the alternator still charges, is that the fields in the alternator are magnetized from the current this wire carries, along with the other red wire in the alternator plug. The fields retain this magnetism when the truck is not running for a period of time until it bleeds off, and then they will have to be recharged. It's called residual magnetism and is similar to what happens when a screwdriver is held with a magnet for a short period of time. If the truck sits for a couple of weeks it may not charge when it is started. On the cab side of the firewall this brown wire becomes a 20 gauge yellow or brown, with white stripe resistance wire, and it is connected to the accessory terminal on the key switch. This wire feeds the internal regulator and tells it how much current to let the red wire feed the alternator fields which controls the alternator output. I'm surprised that you haven't overcharged or undercharged the battery. From your picture it appears that the wire just broke away from the no. 1 terminal on the alternator. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

07-16-2018, 03:44 PM	#4
BRL Registered User Join Date: Jun 2014 Location: Tahuya WA Posts: 510	Re: Ain't This Wire Supposed To Be Hooked Up? Thank you for your help VetteVet! I probably just picked up the plug at a salvage yard and didn't color code anything. I just wrapped up some extended wires with tape and plugged it in. I will shorten the heater hose to provide clearance away from that plug and either fix or replace the plug itself. Again much thanks for the reply.



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