Wiring Problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

oshanahan · 11-22-2007, 02:03 PM

I have a 72 GMC project truck. Everything with the wiring was working fine until I went to pull out the gauge cluster, radio, and heating controls in order to replace the components and repaint the interior. After disconnecting everything, the ignition would not turn. Nothing is getting juice now, including the headlights. The battery is fully charged. I have a wiring diagram but I am still unable to locate the source of the problem. Admittedly, I am a wiring novice. I was wondering if anyone has run into similiar problems or have any "gotchas" that they can let me know about.

Thanks.

J.P. in KC

1972 GMC C1500

FRENCHBLUE72 · 11-22-2007, 02:20 PM

First thing to check since you repainted would be the grounds..

oshanahan · 11-22-2007, 02:38 PM

Thanks for the reply.

I haven't repainted yet. I removed the components and then noticed the problem. Other than hooking the gauge cluster back up I haven't done anything. The strange thing is that the headlights will not work now. That's the confounding thing. I wouldn't think they would have anything to do with the components I removed.
I will re-check the grounds.

*72lb4x4* · 11-22-2007, 04:16 PM

I think some funny things happen with lights if the headlight switch isn't grounded, but it doesn't seem like it would cause it not to turn over.

Assuming you have the mechanical oil pressure guage, you don't want it to turn over or start if you've disconnected the pressure guage. Oil will squirt from the line.

Voltage is measureed to ground...
Indicated voltages are approximate... The farther from the battery, the more possible it is to have a reduction in voltage due to resistance in connectors and grounds.

Measure the voltage at the battery: 12.5V
Measure the voltage at the terminal block on the fender by the battery: 12.5V
Measure the voltage at the terminal block on the firewall (big red wire): 12.5V
Measure the voltage at the red wire on the ignition switch: 12.5V
Measure the voltage at the headlight switch: 12.5V
Measure the voltage at the dimmer switch: 12.5V (maybe only with the light switch on)

Where do you stop finding voltage?

**john** · 11-22-2007, 04:34 PM

Look for a fusible link between the batt and junction block. The 12ga red wire supplies the power. Could be blown link or bad connection. (junction block by batt at top of pic)

11-22-2007, 02:03 PM	#1
oshanahan Registered User Join Date: Nov 2007 Location: Kansas City, MO Posts: 2	Wiring Problems I have a 72 GMC project truck. Everything with the wiring was working fine until I went to pull out the gauge cluster, radio, and heating controls in order to replace the components and repaint the interior. After disconnecting everything, the ignition would not turn. Nothing is getting juice now, including the headlights. The battery is fully charged. I have a wiring diagram but I am still unable to locate the source of the problem. Admittedly, I am a wiring novice. I was wondering if anyone has run into similiar problems or have any "gotchas" that they can let me know about. Thanks. J.P. in KC 1972 GMC C1500

11-22-2007, 02:20 PM	#2
FRENCHBLUE72 PROJECT 7DEUCE Join Date: Dec 2002 Location: GRANTS PASS OR Posts: 21,606	Re: Wiring Problems First thing to check since you repainted would be the grounds.. __________________ GO BIG GREEN GO DUCKS MEMBER #6377 72 k-5 daily driver 6'' lift 35'' 350-350-205 slowly getting rust free. Project "7DEUCE" check out my build http://67-72chevytrucks.com/vboard/s...d.php?t=267665 Tim Powell..R.I.P EastSideLowlife..... R.I.P..

11-22-2007, 02:38 PM	#3
oshanahan Registered User Join Date: Nov 2007 Location: Kansas City, MO Posts: 2	Re: Wiring Problems Thanks for the reply. I haven't repainted yet. I removed the components and then noticed the problem. Other than hooking the gauge cluster back up I haven't done anything. The strange thing is that the headlights will not work now. That's the confounding thing. I wouldn't think they would have anything to do with the components I removed. I will re-check the grounds.

11-22-2007, 04:16 PM	#4
72lb4x4 Account Suspended Join Date: Jul 2006 Location: DFW Posts: 1,427	Re: Wiring Problems I think some funny things happen with lights if the headlight switch isn't grounded, but it doesn't seem like it would cause it not to turn over. Assuming you have the mechanical oil pressure guage, you don't want it to turn over or start if you've disconnected the pressure guage. Oil will squirt from the line. Voltage is measureed to ground... Indicated voltages are approximate... The farther from the battery, the more possible it is to have a reduction in voltage due to resistance in connectors and grounds. Measure the voltage at the battery: 12.5V Measure the voltage at the terminal block on the fender by the battery: 12.5V Measure the voltage at the terminal block on the firewall (big red wire): 12.5V Measure the voltage at the red wire on the ignition switch: 12.5V Measure the voltage at the headlight switch: 12.5V Measure the voltage at the dimmer switch: 12.5V (maybe only with the light switch on) Where do you stop finding voltage?

11-22-2007, 04:34 PM	#5
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: Wiring Problems Look for a fusible link between the batt and junction block. The 12ga red wire supplies the power. Could be blown link or bad connection. (junction block by batt at top of pic) Attached Images __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/



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