91 Suburban dash brake light on

Greets, as the title implies. Before the light came on the truck had a propensity to lock up the back wheels, other than that it seemed to work fine. The light stays on dimmer than when the e-brake is applied. Brake fluid level seems fine.

I am trying to narrow down what could be the culprit- master cyl, proportioning valve, ????

I am selling this truck and don't want to put a lot of money out but I want to fix it first.

Thanks in advance!! :smile:

On the prop valve there is an eclectrcal connector with one wire in it: Unplug the connector and see if the red "BRAKE" indicator on the dash goes out. Post your results.

On the prop valve there is an eclectrcal connector with one wire in it: Unplug the connector and see if the red "BRAKE" indicator on the dash goes out. Post your results.

I an assuming this valve is located on the front of the master cylinder? If so I unplugged the wire and the brake light stays on.

thanks for your help!

Two brake lines leave the master cylinder and go to the proportioning valve. It is usually close to the master cylinder and has 2 lines that go to the front wheels and one that goes to the rear wheels. When you unplug the wire, if the light stays on, the problem is the parking brake is not released, or the park brake switch is stuck. You can confirm that by unplugging the switch on the park brake mechanism.

Two brake lines leave the master cylinder and go to the proportioning valve. It is usually close to the master cylinder and has 2 lines that go to the front wheels and one that goes to the rear wheels. When you unplug the wire, if the light stays on, the problem is the parking brake is not released, or the park brake switch is stuck. You can confirm that by unplugging the switch on the park brake mechanism.


I doubted it was the ebrake switch because when that is engaged the light is brighter. I unplugged it anyways and the light stays on dimly.

Here is a photo of what I think is the proportioning valve attached to the master cylinder. I unplugged the wire going to it and the light stays lit.

I guess I need to pull the rear drums and see whats going on.

Yes, that is the proportioning valve. If it stays lit when both the prop valve and park brake are unplugged at the same time, there might be a problem in the daytime running light circuit, (the DRL's use the same tan with white trace wire). Check the fuses and DRL bulbs and grounds.

Yes, that is the proportioning valve. If it stays lit when both the prop valve and park brake are unplugged at the same time, there might be a problem in the daytime running light circuit, (the DRL's use the same tan with white trace wire). Check the fuses and DRL bulbs and grounds.

I don't think this truck has daytime running lights, also like I mentioned before there was a problem with the rear wheels locking up that has not occured since the light came on. Ugh, I just need to sell this thing and was hoping to fix the dash light before that happened so I can get the most for it.... :disappoin

If the light stays on with both the park brake switch and prop valve unplugged, the brakes are not causing the light to come on. Those are the only two things in the brake system that can turn the light on.

If the light stays on with both the park brake switch and prop valve unplugged, the brakes are not causing the light to come on. Those are the only two things in the brake system that can turn the light on.

Ok, so then it points to an electrical fault somewhere? Its just odd that the speedometer failed and this light started being on at the same time.

Bingo! Most likely a poor ground or short circuit in the cluster itself or the wiring that goes to it. Make sure the connector that plugs into the instrument cluster is plugged in tightly. It's kind of a cheesy set up and can vibrate loose over time. Check all fuses, both terminals, with a voltmeter or test light.

Not real sure if your '91 has rear ABS. If it does and the speedo quit, you may want to look at the VSS (Vehicle Speed Sensor).