Wiring Problems

[oshanahan]

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]

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

[oshanahan]

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]

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]

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)