Brake light problem

[Scooby3242]

I have a 1973 GMC truck and my drivers side brake light will not work. I chased problem all way to the firewall where the tail light harness plugs in before going into the firewall. It appears the passenger side uses the green wire and the drivers side uses a yellow wire that is not getting power. Any ideas? The only other thing i could think of is maybe the brake switch connected to the peddle. i believe it has a orange and white wire but not sure if that effects the difference between the driver and passenger brake light.

 

[gpmorgan]

I think the yellow wire gets its power from the combination switch. I could be wrong. Did you check the ground for that side?

 

[Scooby3242]

no I did not check the ground but the tail light works when the headlights are on, is there a separate ground for the tail light and brake light?

 

[gpmorgan]

I think they use the same ground. Do all the other lights work?

 

[Scooby3242]

Well the dash lights don’t work and the cab light doesn’t work . Not sure if they are connected somehow


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[spanky55amg]

http://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

could check out the wiring diagram. I havent seen this one, but the one for the 1984 is pretty detailed.

 

[Honky Kong jr]

Do the turn signals work?

 

[Scooby3242]

Do the turn signals work?

Yes turn signals work and so do the flashers


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[Honky Kong jr]

Yes turn signals work and so do the flashers


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Do you have continuity in the wire for brake lights from front to back.

 

[Scooby3242]

I didn’t check, the only thing I have used is a test light. I have a multi meter but I will need to figure out how to check continuity with the meter.


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[Honky Kong jr]

I didn’t check, the only thing I have used is a test light. I have a multi meter but I will need to figure out how to check continuity with the meter.


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That’s what I’d start with you can put the common ( black) lead to the frame and back probe the brake wire at the bulk head connector if you have continuity it’s shorted to ground and could be rubbed threw somewhere

 

[Scooby3242]

Do you have continuity in the wire for brake lights from front to back.

I did check the plug at the firewall with a test light and there was no power coming out from the cab on he yellow wire that goes to the drivers brake light. The green wire that goes to the passenger brake light has power tho. Not sure if that matters. I tried looking at the wiring diagram and I think the test I did was right but that diagram is hard to read


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[Scooby3242]

That’s what I’d start with you can put the common ( black) lead to the frame and back probe the brake wire at the bulk head connector if you have continuity it’s shorted to ground and could be rubbed threw somewhere

I’ll try that


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[Honky Kong jr]

I did check the plug at the firewall with a test light and there was no power coming out from the cab on he yellow wire that goes to the drivers brake light. The green wire that goes to the passenger brake light has power tho. Not sure if that matters. I tried looking at the wiring diagram and I think the test I did was right but that diagram is hard to read


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It still might be shorted to ground I’d check it like I described.

 

[Scooby3242]

It still might be shorted to ground I’d check it like I described.

Will do thanks


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