68 GMC wiring issue (Brake/turn lights) HEP!

[Bubba_s]

Been trying to find the issue with the brake lights and turn signals in my buddies 68 truck. Wiring from the firewall back is Ok, brake switch has power and works. I believe I have isolated the problem to between the output of the brake switch and the firewall (where the lines exit the cab and go to the rear). All fuses are Ok, replaced the flasher module. Any help or thoughts on this would be greatly appreciated. I have a schematic but am having a little trouble fully understanding it.

Can you hep?

 

[Ol' Gravy Leg]

Check your wires for continuity to ground (make sure there's not a short). Sounds crazy, but throw some contact cleaner on the bulb socket and interconnects. A bad connection will make things appear lewy.

 

[Bubba_s]

Yeah, the bulbs are OK, I have bypassed the issue area and confirmed they work. I think it is a grounding issue, I just have to get a better idea of the wire paths. I really thought this would be easier! :loco

 

[fawndog]

What is the problem you're having ?

 

[TheRobSJ]

Two words. Maybe three actually.

Voltage drop test.


Measure available voltage at battery terminals for baseline. Then measure voltage across bulb socket terminals with light switched on. In a good system, damn all all of the voltage will read there. If you're getting much less or zero, then there is voltage dropping across some resistance elsewhere in the circuit. You can measure for voltage drop across sections of wire, switches, etc to find where the resistance is.

 

[Bubba_s]

What is the problem you're having ?

No brake lights or turn signals (same filament in same bulb). I jumpered a wire directly from the brake switch to the line heading out of the cab and it worked.

Headed to the net to search "measuring voltage drop" :laughing

 

[Bubba_s]

not helping in my troubleshooting is the obvious evidence that someone, at some time did some 'rewiring' though it may not actually be involved in the circuit I am looking at...

 

[fawndog]

Are you missing hazards too ?

How are the contacts on the turn signal switch ?

 

[Bubba_s]

Are you missing hazards too ?

How are the contacts on the turn signal switch ?

Yes sir. How difficult is taking off the steering wheel? I am assuming that would need to be done to check those contacts...

 

[fawndog]

quick and dirty
Key on engine off
Move the turn signal lever up and down, while holding forward and then back, did anything light up ?

 

[Caddywumpus]

HEP. This is the wrong section.

 

[Bubba_s]

HEP. This is the wrong section.

But I'm getting Hep!!

Going to do the quick and dirty check ASAP, thank you And thanks for all of the responses thus far!