72 GMC Brake light Probems
 

Hey guys I'm a senior in High School. Im redoing my 72 GMC C20 after it blew up. I'm currently tackling wiring. I bought the American Auto wire redo Kit, All seems to be going well. I got the engine, turn signals, headlights etc. done. (for some reason the brights don't work but I haven't investigated much they might just be burnt out). last night I figured id tackle the brake lights. Both of the side marker and park lamps work (the dim brake light) both of the turn signals work. but here's where it gets weird. Only the passenger brake light comes on when the pedal is pushed. WTF??? It cant be my wiring because the turn signal works, it cant be the brake switch because the passenger side works, My only thought is something isn't right in the fuse box which comes pre assembled. If your not familiar with the wiring set up their are 4 wires. brown- park lights (dim brake lights) green passenger turn/brake, yellow- driver side turn/brake, and light green-reverse lights. Any thoughts what so ever would be much appreciated thanks guys!
Colton

Re: 72 GMC Brake light Probems
 

I just installed this same kit on my GMC without any issues.

You might want to check the rear connector to make sure the rear connector is making contact properly. Also, start from the connector in the dash and measure the voltage to ground on the yellow wire with the brake pedal pushed, then check it back at the rear connector and then check it at the light bulb housing. Always measure it to ground. These male and female connectors can get folded over in the housings also if you are not careful.

Re: 72 GMC Brake light Probems
 

Check the plug at the steering column connector. When you step on the brakes, the white wire from the brake switch energizes up the steering column. From there it goes through the TS switch and powers up both the yellow and green wires going to the respective bulbs. So check the yellow wire at the connector when you push on the brake pedal. You can also alligator clip a powered jumper lead to the yellow wire with the plug disconnected and see if you have a brake lamp. May have a bad turn sig switch

Re: 72 GMC Brake light Probems
 

You were absolutely right! it was the white wire (bad connection). Thanks A lot!!!! much appreciated.