Brake warning light issue

[Slowleak]

My brake warning like has never activated when the ignition key is turned. I understand that it should be on temporarily either when the key is first switched on, or maybe when turned to start. I have tested it by grounding the wire at the proportioning valve and the light does work, just not when i turn the key.

Anybody know what triggers it to activate when the key is turned? Should it ground in the switch when the key is moved to start?

 

[75junebug]

I dont think they light up when the key is turned on like modern vehicles. The trigger is on the proportioning valve, and I believe it only lights up if the "piston" inside moves off center, which indicates a loss of fluid going to the front or rear lines.

 

[Slowleak]

I dont think they light up when the key is turned on like modern vehicles. The trigger is on the proportioning valve, and I believe it only lights up if the "piston" inside moves off center, which indicates a loss of fluid going to the front or rear lines.

Thats what i always thought but someone told me it should light up briefly. I just found my owners manual and it says "the brake warning light should glow briefly when you turn the ignition lock cylinder to START with your foot off the brake pedal"

 

[half cab]

My '76 lights up briefly when u hit the starter. May be at the ign switch your trouble might be?

 

[kip60]

Might have something at the ignition, but more than likely the brake sensor has failed. I think that's what most people have trouble with.

 

[Slowleak]

Thanks guys. I checked the wiring and tested continuity thru the valve switch. It all looks good and the light works if i ground the wire that is plugged into the ignition switch with the switch on. Looks like a bad ignition switch or bad ground. Lemme just get back up under that dash for a bit.......

 

[Viperwolf1]

The brake warning light wire goes to the proof terminal at the ignition switch. That terminal is supposed to go to ground in START. Now that depends on the integrity of the ignition switch and the continuity to ground where the switch meets the dash. I have seen new ignition switches that did not ground that terminal in START. This has absolutely nothing to do with the warning sensor.

 

[Slowleak]

I have tested all the wiring. I may be wrong but i think the brake sensor has to be connected for the light to come on when starting. One wire at the valve is grounded when the key is off. I don't know if that is normal or not. I have continuity between the terminals on the brake switch itself which seems right.

I think its down to the ignition switch or ground. I am not getting continuity to ground from the terminal on the ignition switch when the key is turned to start. The switch appears to be grounded, at least i get continuity from the key cylinder and the switch face. Any ideas about how to test the switch for ground without pulling it out? I was hoping it had a ground wire.

 

[Viperwolf1]

There is no ground wire. The cup behind the dash needs to have good contact with the metal of the dash. You could remove the switch then try to clean those areas up.

 

[Slowleak]

Made a few edits for clarification. I think i will pull the switch tomorrow. Thanks

 

[DirtDonk]

did you verify that the bulb was still working?

Paul