My 1987 IROC's parking brake switch seems like it's "on" all the time. I'm pretty sure that when the parking brake handle is up (out of the stowed position) that the switch connects to ground and sends a ground signal to the instrument cluster to light up the brake light.

My car is under construction (see signature) and the cluster has been replaced with a Holley 12.3 ProDash. I want to program the ProDash to light up "BRAKE" when the parking brake handle is up past the stowed position. This will help keep me from driving off with the parking brake engaged even slightly like I did recently with my LS swapped Foxbody coupe in my signature.

Currently, I"m getting a ground signal from the switch whether the handle is stowed or out of the stowed position. I get continuity from the switch to the connector at the instrument cluster in any parking brake position. Any suggestions on this?

 

unplug the switch and see if there's continuity on the chassis from the switch with the brake off vs on. it's normally open so that should read OL on the meter. if the switch is working then the circuit has gone to ground somewhere along the way.

 

Might want to make sure it's not the switch in the proportioning valve. Unplug that and see if the light goes out.

 

oh that's a good "dumb" thought, there's 2 lights one for that warning and the other for the parking brake. I was thinking parking brake but you're probably correct. check brake fluid level first then look at the trigger switch on the valve. unplug that to verify.

 

I think not. One light, two things that can trigger it.

 

Hey guys, thank you for all the replies.

According to my "Brake Warning System" schematic, there are three things that will ground and turn on the brake warning light. 1. Brake pressure switch with unequal brake pressure, 2. Ignition switch in "bulb test" and 3. Parking brake switch when the parking brake is applied:




1. At the moment, my brake pressure switch wire is disconnected. All wires from the C100 are currently out of my car The brake pressure switch is pinned at B2 in the C100 connector. With the wire not connected to the B2, I wouldn't think that I'd get a ground

2. At the moment, my steering column is out of the car as I'm finishing up clutch pedal and neutral safety switch wiring so there should be no ground coming from the ignition switch.

3. I've got my center console put back together but I'm going to have to take it back apart. When I was playing with the parking brake switch, it seemed to be all metal. In other words, metal to metal. It appeared to me like it would be grounded no matter what position the parking brake handle was in. I'll look at it again.

 

I took my car's center console back apart today to get to the parking brake switch and see what I could find while using my multimeter. I had previously mentioned that the switch was connecting to ground when the handle was up or down. What I found was that the switch was always "closed" and causing a ground. The switch is held on by one bolt and there is some play there. I moved the switch and tightened it back down and now it works like it should.


This is the reading now with the parking brake handle down.



This is the reading with the parking brake handle out of the stowed position.

When I check continuity between chassis ground and the parking brake switch wire, I get this on my Fluke meter:


4.23 million ohms. It should read 0.L but maybe this is close enough ? What do you guys think? Will this be enough ground to erroneously trigger my brake light?

So the switch is now working like it should so at least I made some progress.

 

RTFM, must I do lol

 

Glad you made progress @dannyual320 and reported back! We all need a sanity check now and again lol

 

THIMK... use your knowledge of simple electricity... 12V through 4.3 Mohms = ~ 3 ľA. 3 MILLIONTHS of an amp. No incandescent light bulb will light VISIBLY with that little current passing through it. So yeah, even though it doesn't quite read OL (OverLoad; which is not really an "overload" for ohms, butt since the ohmmeter function on a DMM is actually a voltmeter in parallel with a current source, then if the voltage developed across the impedance under test exceeds the voltmeter's range, then it reads OL) it's PLENTY close enough.

So, you've got the schematic. There's 3 things that can light the light (sorry, I forgot about the Start "bulb check", which does the same thing to the Brake light that it does to the Temp light or gauge), plus the hatch release which relies on the grounds from those 3 things to disable the hatch from opening, so unplug all 3, and pull the hatch relay. Might need to take the tan/white out of the ign sw plug and plug the plug back in so that it can work all the rest of its functions. If the light doesn't light then the wiring and whatnot is all good. Plug each of the other things back in until you find which one lights the light. Then at least you know what you need to be working on instead of being in "maybe it's this maybe it's that maybe it's the aliens again" territory.