Another brake warning light question... (1 Viewer)

[Tim71FJ40]

Ok. I have read several posts on the brake warning light, and I have the following diagram. This makes complete sense to me, except in one specific circumstance. Let me ask the quesiton of what SHOULD happen, then someone can relate it ot hte diagram for me.

Assume I pull the emergency brake with my foot OFF the brake pedal - The e-brake switch closes, and the normally closed presusre switches apply ground and the dash light comes on. This is what I would expect.

However, if wired like it shows below if I pull the emergency brake and then step on the brake pedal it looks like the light would go OFF (assume the key is on). The e-brake switch would close, but the pressure created by stepping on the brake would open the pressure switch, therefore no ground.

I would think that the light would be on anytime the e-brake is pulled with the key on.????

It seems like this would be the case if the right hand wire from the e-brake switch ran directly to ground instead of to the pressure switches. Then the pressure switches would work in conjunction with the brake switch, but the e-brake would always override the circuit when it was pulled.

I don't know how it is SUPPOSED to behave so relating it to the diagram isn't easy.

 

[DSRTRDR]

I would think that the light would be on anytime the e-brake is pulled with the key on.????

this is how it should be

it will not matter whether or not you use the foot pedal brakes while the handbrake is pulled, the light should stay on - even when driving; BTDT

 

[subzali]

the light will go out when you push on the brake. Freaked me out a couple weeks ago when I thought a bulb was burned out.

 

[DSRTRDR]

the light will go out when you push on the brake. Freaked me out a couple weeks ago when I thought a bulb was burned out.

shouldn't - something is wired wrong

 

[DSRTRDR]

Stale Ale was correct - deleted before I could quote

 

[subzali]

shouldn't - something is wired wrong

Stale Ale was correct - deleted before I could quote

I don't think so:
https://forum.ih8mud.com/40-55-series-tech/511958-electrical-problems-99-solved.html#post6904512

 

[DSRTRDR]

I can only tell you how my truck came from factory as far as brake light warning wiring goes - his being a '71 would be the same

 

[subzali]

What part of your truck has Painless Wiring in it?

Just looking at the wiring diagram above (which I'm assuming is correct for '71/'72) as well as the one in the link, it's clear that the pressure switches control the ground path. So if they are open, no light. They open when brake pressure is applied.

If the light is still on when your brake pedal is depressed, then you have an alternate ground path elsewhere in the circuit, or you have a problem with brake pressure/fluid level which is allowing one or both of the pressure switches to close.

 

[DSRTRDR]

the brake/hazard/blinker circuit is in OEM configuration - there is no difference to the OEM wiring diagram except using wire manufactured by Painless

 

[Tim71FJ40]

Agree that according to the diagram I posted the light will go OFF when the brake pedal is depressed - not sure if it is suppoed to, but that's how the diagram is set up. However I think you could make it work the way Claudia suggests by taking the e-brake switch wire directly to ground. Then if teh e-brake is applied it doesn't matter what the pressure switches or the brake pedal are doing, the light will stay on.

I just didn't know if by doing this I was altering the intended functionality of the light.

 

[Tim71FJ40]

Just read Matt's link in post #6. Confirmed - the light should go OFF when emergency brake is set and the brake pedal is depressed. Interesting way for it to work...

 

[Tim71FJ40]

Without it wired this way, there would be no way to test the pressure switches. If they failed OPEN you would never know because the light would never come on. With the e-brake pulled and the light on you prove NO PRESSURE = CLOSED (because light is on), then with foot on brake you prove PRESSURE = OPEN (because light is off).

It's a pressure switch checker.

Thanks everyone!

 

[bj40green]

Hi Tim,

Have look here to see how this system works: https://forum.ih8mud.com/40-55-series-tech/511958-electrical-problems-99-solved.html#post6904512

Rudi

 

[Gredon3]

im going throught this now, both pressure switches are open and I cant get new pressure switches here in Australia