'91 S15 Jimmy parking brake warning light is on constant

The switch that controls the parking brake light is mounted down on the bracket near the floor where the pedal is mounted.

There should be a black switch with a plunger that moves in and out when the pedal is depressed. It will have at least two wires attached to this switch.

Not sure about this light being "on" and then gets brighter when the pedal is depressed. It is either "on" or "off" normally. Could just be a defective switch. It is either mounted with a screw through a mounting tab or the entire switch screws in and out of a round hole in the bracket, in that case you have to pull the plug that the wires are attached to off the back of the switch before removing it.

Hope this helps...

Thanks, I'll check that out. So more than likely is this the source of the problem? Is it a normally open switch? In other words would disconnecting the wires cause the light to go out?

BTW I suppose the reason it gets a bit brighter when depressed is if the switch where corroded, making some contact through the corrosion (resistance) and then when fully depressed, full contact is made.

This could indicate a failure in the hydraulic system. Check fluid level and check for leaks.

Steve

Thanks like I said in my message above, the fluid level is fine. If I had a leak wouldn't it be down?

Not necessarily...

I just read that it could also mean there is a problem with the ABS light circuit. Does the ABS light come on when you turn the key on? If so that's not the problem. So it also comes on when the p-brake switch is grounded out. Unplug the switch and see if the light goes out (the switch is above the peddle). The other way the light can set is by the "combination valve differential pressure switch".

Steve

No ABS light does not come on.

Should the light go out just by unplugging the switch? Or do I need to ground it or short the leads?

Where is the "combination valve differential pressure switch"? How do I check it?

I assume from your message above that problems with leaks could mean low pressure i.e. leaking just enough to cause low pressure but not enough to have noticeably low fluid level?

Thanks for your help.

If your saying the ABS light is NOT coming on when you turn the key. ( it should come on when you turn the key to start the engine, then go out after a second or two once the engine starts) Then you have a problem in the ABS system, check for a blown fuse.

If the '91 has the same setup as my '89 w/rear ABS it would set mystery codes when ever damp, wet or snowy winter weather came in. No ABS light on the '89 , the brake light was used. Codes would say bad solenoid, reset and would be fine for awhile. Never a prob. in summer only winter. My brother's got the truck now w/over 170k miles and the last 2 yr. it hasn't set the ABS code but he hasn't been going up to the north country in the mega salt either.

Exactly, if the ABS light does NOT come on when you turn the key forward, before startup, then the brake light comes on to tell you there is a problem with the ABS light circuit.

Steve

Read my other post from about 2 minutes ago regarding the ABS light.

If the brake light switch is sticking, then unplugging it will "unground" the lead, causing the light to go out. If that is the problem.

Not sure, probably on the master cylinder, or very close to it.

Exactly. :)

Thanks guys, I'm not sure if I ever remember it coming on but that doesn't mean that it did not. I'll go check the fuses.

Thanks

Yes it is winter here with plenty of salt! Any way to clear this other than getting the truck some place warm?

Just checked it again. The ABS light is definitely NOT coming on. I did see it flicker once in the half dozen times that I tried starting the car, so I am pretty sure the bulb is OK.

I checked for fuses and could find none labeled ABS, there was one called Brake but it appears to be fine.

Hrm, do this. With ignition off, short terminals "A" and "H" of the ALDL connector (should be under the steering wheel in plain sight). It looks like terminal "A" is the top right hand corner one, and terminal "H" is the second from the left on the bottom row.

see "12 pin US style") Using a paper clip is popular. Turn ignition to ON position, do not start the vehicle. Watch ABS light, count flashes, report back. ;)

Steve

Will do tomorrow evening. Thanks.

What is the circuit on the link that you sent? Can I use a laptop to dignos the system?

Yes, the circuit is the device you need to build to connect a laptop to a GM ALDL 8192 baud diagnostic port. Your vehicle is an ALDL 160 baud I believe, and requires a different circuit. But this wouldn't help you in your situation. Just getting the codes will help enough.

Steve

OK the ABS light does not flash. It does not come on at all but the check engine light flashes.

Here is the sequence:

Brake Light on constant.

Check Gauges on constant.

Check engine flashes - one short flash no light (about 1 second) then 2 short flashes.