My red brake warning light is on and will not turn off. The brakes work fine, but I was hoping to develop an understanding of what might be causing this. What conditions should I ordinarily expect to cause this light to turn on? I suspect that in ordinary circumstances, low brake fluid triggering the sensor at the bottom of the brake fluid reservoir could cause the light to come on. Otherwise, if the parking brake is engaged, I would guess that would trigger the light to come on. There is plenty of brake fluid in the reservoir, and the light stays on when my parking brake is engaged and also when it is disengaged.

I recently replaced all of the parking brake cables and got that up and working. I noticed after fixing it that the brake warning light never would come on, even when the brake is engaged. I noticed this past Saturday that the brake came on and seems to stay on no matter what. I suspect there may be a problem with the little electrical connector on the parking brake that detects when the parking brake is engaged.

Please let me know your thoughts on what circumstances would ordinarily cause the light to turn on and ideas on what might be causing the problem.

 

ohm out the switches with a meter
might be ebrake since thats last you touched

 

Red light as in light that says "brake"? My light was just stuck on too, was the e brake switch that went bad. Got a new switch from rock auto and all is fine now. Think it had something to do with my cruise control shutting off too because after I changed the switch there has been no issues with that anymore. Could be non related though. My switch went through several stages of death. Stuck on, flickering when driving and then totally dead with ebrake on.

 

Yes, the light is red and reads "BRAKE (!)(P)".

 

Alright, here is where I would ordinarily just fire up the old parts cannon and replace things until the problem goes away. But, I think it would be a good idea for me to step through this the correct way.

So, I got out my multimeter and set it to the lowest resistance setting. I put the red lead on the blade on the switch where the wire connects to it, and the other to the little bolt where it mounts to the brake assembly. Regardless of whether the parking brake pedal is depressed or not, I get little resistance, much less than 1. Should I expect the resistance to be 1 when the parking brake is fully up and then very little when the parking brake is depressed? Please have some patience with my ignorance here, but what is the smoking gun I am looking for that would tell me that the switch is bad? I have never actually gone through the process to "ohm out" a switch, instead favoring the trusty parts cannon.

 

if its staying on 1 ohm, that means its contacts are not opening up
should be high ohms (open) at one position and low ohms (closed) at the other position

 

Alright, I found some documentation. Here is the guidance offered in the manual for the issue I'm facing.

I know the fluid level is not low and is not leaking and the brake fluid level indicator should be close to brand new if that's the electrical connection on the brake master cylinder. I replaced the brake master cylinder and attached reservoir recently. So, we're basically down to an electrical issue, because the light stays on when the parking brake is released.

Here is the electrical diagram for the warning light.



I just tested the park brake switch, and it appeared to be closed, thus completing the circuit to ground, no matter what position the parking brake lever is in. This seems to me to confirm that the park brake switch has failed.

 

Just unplug connector. The light should go off.

 

try unplugging the switch. if the light goes out. you found the problem.

 

I unplugged the connection at the park brake switch, and the light does not go off. I would expect that to open the circuit just as if the switch was open with the pedal up. That tells me that the problem is something else, I guess, but I'm not sure what else it could be. Could low vacuum cause the brake warning light to come on? The brake pedal does not feel stiff when the engine is running like you might expect if the pump is not making enough vacuum. Could the "low vacuum warning switch" referenced in the diagram have failed?

 

If I remember right, a vacuum pump that is failing can set the light in the dash. So a bad vacuum switch could set the light also. Have you tested the vacuum pump with a gauge? You should see at least 50 inches, if I remember right.

 

yes low vacuum will turn the light on.

 

I'll go get a vacuum gauge tomorrow.

 

I started the truck this morning and the brake warning light turned off when I started the truck. I tried to pay close attention to how the pedal felt, and it seemed to me that I could tell a subtle, positive difference in the brake pedal. After a little bit of driving, the brake warning light became illuminated. I again tried to pay close attention to how the pedal felt, and it seemed to me that I could now tell a subtle, negative difference in the brake pedal.

I will get a vacuum gauge to do some testing. My hypothesis is that the vacuum pump performed better in the cold ambient temperature and good enough to exceed the threshold for the vacuum switch. Then, as the engine and vacuum pump warmed during driving, the vacuum pump began to perform poorly, now unable to generate enough vacuum to meet the threshold for the vacuum switch, which illuminated the warning light.

I am biased here because I happen to have a new spare vacuum pump and new pulley in the toolbox ready to go, so I kind of want that to be the problem. Does anybody have any thoughts that differ from mine?

 

Your theory make sense to me. But testing the vacuum when cold, and again while warm would probably confirm it.