Brake light issue.

[URSATDX]

M35A3 dual circuit brakes.

Directional and hazards work fine. Jump the leads from the air pack light switch and brake lights come on.

Continuity test on the air brake light switch reads fine.

Connectors appear solid and are tight on switch pins.

Common sense (not my strongest trait) says they should work as I have power and continuity.

Any thoughts would be much appreciated.

 

[cattlerepairman]

Did you have soldier B depress the brake pedal while you measured continuity? Because otherwise, there should be no continuity; switch is open. If you get continuity with the brake pedal depressed and the lights work when you jump the terminals then, good grief, the lights ought to work!

 

[URSATDX]

Tested both switches and jumped both sides.
Soldier B pressing brake pedal and continuity on both switches, lights come on when jumped on both sides.
After doing the passenger side testing the brake lights worked with the pedal for about 45 seconds. Off and on
maybe 5 times with the last 2 cycles the lights got dimmer and then nothing. I have disassembled and inspected
the turn signal switch assy and it appears like new inside and functions properly. I removed and cleaned the mounting bolts
on the tail light assemblies to see if it may be a grounding issue with the bolts. Nothing.
Schematics are not my forte but I will, again look at the TMs to see if I am missing something.
Thanks for any suggestions and replies.

Did you have soldier B depress the brake pedal while you measured continuity? Because otherwise, there should be no continuity; switch is open. If you get continuity with the brake pedal depressed and the lights work when you jump the terminals then, good grief, the lights ought to work!

 

[frank8003]

Last I seen this problem drove us nuts. Guy replaced the dash switch controller, not the turn signal controller.
That did not fix it either.
You do have a real one of these, right?

 

[URSATDX]

Light switch removed disassembled, looks new, dated 1991.
Still digging.
Thanks again for all the responses.

 

[glcaines]

If your brake lights come on when shorting across the switch terminals, but not when pedal is pushed, you have a switch problem.​

 

[URSATDX]

That's what I figured. But.
Both switches test good for continuity when there is adequate air pressure and the pedal is pushed.
Brake lights are activated when I short the leads. But.
No brake lights when I push on the pedal and all is back together.
Out of time for today.
I'll probably remove/test/replace the switches and replace the switch connectors that come from the harness.
Love the truck but she is a B!tch.

glc: cant read your response as the font is grey or black.
Thanks for the response.

If your brake lights come on when shorting across the switch terminals, but not when pedal is pushed, you have a switch problem.​

 

[Back2Wyo]

I had a motorcycle that had a problem with the brake switch on the front handlebar. It would check fine with an ohm meter but it would not pass voltage to the light. Replaced the switch and that fixed the issue.

 

[URSATDX]

Thanks B2Wyo
Was thinking the same.
Thanks for the replay and I love Jackson Hole.

I had a motorcycle that had a problem with the brake switch on the front handlebar. It would check fine with an ohm meter but it would not pass voltage to the light. Replaced the switch and that fixed the issue.

 

[frank8003]

This one drove me to replace the switch and run an LED to the cab so that whenever the brake light switch functions the LED in the cab glows. It does not prove that the back lamps actually illuminate but does prove the switch is functioning. It works to my satisfaction. The Led was 99 cents.


This switch is for the air side done on a M35A2

 

[URSATDX]

Ordered 2 switches and some new connectors.
Wish I could buy some time, too.
Thanks for the help.

 

[URSATDX]

Replaced driver side switch and new connectors.
Brake lights working.
Thanks to all.

 

[cattlerepairman]

Thanks for providing the update! It is annoying later on to find problems without solutions.