Painless Wiring - Backfeeding from Alternator solved *diagram* - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Hardway · 11-30-2007, 07:02 PM

I was running in to what appears to be a common problem when replacing the factory harness with an aftermarket harness such as Painless or other company. There have been posts about this before but basically you will run in to a situation where your truck will start and run but will not turn off when the key is switched to off. If you have a 3-wire alternator and have wired up everything according to the Painless manual that is included for out trucks then you have probably run in to this problem. Several members have mentioned running a diode or small bulb to remedy the problem. My only question is, where to run it and what value diode do I need? After some searching I found the answer on a Jeep site that uses a page from the Jeep Painless instructions. This is the same diagram found on page 6 of the Painless instructions for our trucks but omits the information about the diode. I figured this would save some time for members in the future.

ChevLoRay · 11-30-2007, 07:29 PM

Hope it works for you. I used a harness from M&H Electrical Fabricators. No problems.

jlaird · 11-30-2007, 08:17 PM

so i'm assuming there is no issue with a 1 wire alternator?

joelanickerson · 11-30-2007, 08:27 PM

Good one. I nominate this for the Technical FAQ

webfoot · 11-30-2007, 08:31 PM

If you unplug the 2-wire connector does the engine shut off? That would definitely isolate the problem. You upgrading to an internally regulated alt I assume? I did this on my 70 chevelle and did not have to include a diode. Did you jumper 2 of the wires together from the voltage regulator?

Hardway · 11-30-2007, 08:48 PM

The truck already had the int. reg. 3-wire alternator on it and everything was working fine before I installed the new harness. The reason I got the new harness was because a wire grounded against the back of the dash cluster and melted part of the harness for the rear back up lights and amp. gauge.

I do not think you would run in to this problem with a one wire alt. but do not quote me on that.

If you unplug the connector it will shut the truck off with the key in the off position. This is appearantly a well known problem for anyone using a GM 3-wire internally regulated alt. If you are using an external regulator then you may not run in to this problem. I Google'd "back feeding from alternator" You would be surprised of how many hits you get.

webfoot · 11-30-2007, 08:50 PM

I will take a pic of how mine is wired up, if you want.

Hardway · 11-30-2007, 09:03 PM

I would love to see it. The more pics and diagrams the better for all of us.

webfoot · 11-30-2007, 09:31 PM

Here's a couple of diagrams to chew on while I find my digi cam.

They are slightly different but will both get the job done. I used the first one.

**VetteVet** · 12-01-2007, 12:07 AM

Item two explains it pretty well.
http://www.6066gmcguy.org/charging.htm

11-30-2007, 07:02 PM	#1
Hardway Registered User Join Date: May 2007 Location: Cedar Park, TX USA Posts: 52	Painless Wiring - Backfeeding from Alternator solved diagram I was running in to what appears to be a common problem when replacing the factory harness with an aftermarket harness such as Painless or other company. There have been posts about this before but basically you will run in to a situation where your truck will start and run but will not turn off when the key is switched to off. If you have a 3-wire alternator and have wired up everything according to the Painless manual that is included for out trucks then you have probably run in to this problem. Several members have mentioned running a diode or small bulb to remedy the problem. My only question is, where to run it and what value diode do I need? After some searching I found the answer on a Jeep site that uses a page from the Jeep Painless instructions. This is the same diagram found on page 6 of the Painless instructions for our trucks but omits the information about the diode. I figured this would save some time for members in the future. Attached Images __________________ Jeff's Current Vehicles: 1989 Turbo Trans Am Pacecar "Life is like racing, it goes by fast and has many turns"

11-30-2007, 07:29 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Painless Wiring - Backfeeding from Alternator solved diagram Hope it works for you. I used a harness from M&H Electrical Fabricators. No problems. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

11-30-2007, 08:17 PM	#3
jlaird Senior Member Join Date: May 2004 Location: johnstown, NY Posts: 2,393	Re: Painless Wiring - Backfeeding from Alternator solved diagram so i'm assuming there is no issue with a 1 wire alternator?

11-30-2007, 08:27 PM	#4
joelanickerson Registered User Join Date: Jun 2007 Location: Denton tx Posts: 19	Re: Painless Wiring - Backfeeding from Alternator solved diagram Good one. I nominate this for the Technical FAQ

11-30-2007, 08:31 PM	#5
webfoot Registered User Join Date: Nov 2007 Location: Hermiston, OR Posts: 947	Re: Painless Wiring - Backfeeding from Alternator solved diagram If you unplug the 2-wire connector does the engine shut off? That would definitely isolate the problem. You upgrading to an internally regulated alt I assume? I did this on my 70 chevelle and did not have to include a diode. Did you jumper 2 of the wires together from the voltage regulator? __________________ *Running in place gets you nowhere fast.* -me 1968 GTO 4-spd covnvertible 1970 K-20 4-speed, factory AC. Last edited by webfoot; 11-30-2007 at 08:33 PM.

11-30-2007, 08:48 PM	#6
Hardway Registered User Join Date: May 2007 Location: Cedar Park, TX USA Posts: 52	Re: Painless Wiring - Backfeeding from Alternator solved diagram The truck already had the int. reg. 3-wire alternator on it and everything was working fine before I installed the new harness. The reason I got the new harness was because a wire grounded against the back of the dash cluster and melted part of the harness for the rear back up lights and amp. gauge. I do not think you would run in to this problem with a one wire alt. but do not quote me on that. If you unplug the connector it will shut the truck off with the key in the off position. This is appearantly a well known problem for anyone using a GM 3-wire internally regulated alt. If you are using an external regulator then you may not run in to this problem. I Google'd "back feeding from alternator" You would be surprised of how many hits you get. __________________ Jeff's Current Vehicles: 1989 Turbo Trans Am Pacecar "Life is like racing, it goes by fast and has many turns"

11-30-2007, 08:50 PM	#7
webfoot Registered User Join Date: Nov 2007 Location: Hermiston, OR Posts: 947	Re: Painless Wiring - Backfeeding from Alternator solved diagram I will take a pic of how mine is wired up, if you want. __________________ *Running in place gets you nowhere fast.* -me 1968 GTO 4-spd covnvertible 1970 K-20 4-speed, factory AC.

11-30-2007, 09:03 PM	#8
Hardway Registered User Join Date: May 2007 Location: Cedar Park, TX USA Posts: 52	Re: Painless Wiring - Backfeeding from Alternator solved diagram I would love to see it. The more pics and diagrams the better for all of us. __________________ Jeff's Current Vehicles: 1989 Turbo Trans Am Pacecar "Life is like racing, it goes by fast and has many turns"

11-30-2007, 09:31 PM	#9
webfoot Registered User Join Date: Nov 2007 Location: Hermiston, OR Posts: 947	Re: Painless Wiring - Backfeeding from Alternator solved diagram Here's a couple of diagrams to chew on while I find my digi cam. They are slightly different but will both get the job done. I used the first one. __________________ *Running in place gets you nowhere fast.* -me 1968 GTO 4-spd covnvertible 1970 K-20 4-speed, factory AC. Last edited by webfoot; 11-30-2007 at 09:32 PM.

12-01-2007, 12:07 AM	#10
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,703	Re: Painless Wiring - Backfeeding from Alternator solved diagram Item two explains it pretty well. http://www.6066gmcguy.org/charging.htm __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.



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