Parking Brake Light Not Coming On

[legozombie]

Good Evening. I am trying to trouble shoot my brake light not coming on on my dash. I have never seen it on once and never again. I have new bulbs + sockets and know that the bulb is working because I have bench tested each light and gauge for functionality so, I know it's not the bulb unlike this thread -> (https://www.gmsquarebody.com/threads/parking-brake-light.38771/). I don't know if it's appropriate to create a new thread or if I should have continued that aforementioned one.

What are my next steps? Based on my research on these forums there's the parking brake lever switch (I don't know how to test this) and there is also the proportion/combo valve thing that can change the state of the "Brake" light on the dash. Any ideas on identifying the next logical troubleshooting steps? As stated, I would like to test the parking break but don't know how. Next thing to check I presume would be to check the prop/combo valve thing. Thanks a (3/4) ton!

 

[mtbadbob]

12v stab tester to parking brake switch, should be 2 wires. Once switch is depress, it should open the circuit to send 12v power to light on dash. Test both wires in both the released position, and set position.

 

[Jgonick]

The light should come on when one of the three tan/wht-33 wires is grounded. They are at ignition switch (when you start the truck), parking brake, and brake pressure differential valve(changes to tan-33). It would be easy to unplug it from the parking brake and ground the wire to test.

It is fed current by a pnk/blk-39 wire that goes to the instrument cluster. I would check the cluster connection and also make sure the bulb socket is making good contact with printed circuit.

I'm sure you checked the fuse- gau/idle I think.. If the fuse was bad there would be other things not working, but it wouldn't hurt to check.

 

[legozombie]

12v stab tester to parking brake switch, should be 2 wires. Once switch is depress, it should open the circuit to send 12v power to light on dash. Test both wires in both the released position, and set position.

So I found sometime last week to do a quick test. The switch only had one wire that was brown/tan with a white stripe and it essentially just connects the circuit to the ground. This is looks like it's done by screwing into the parking brake assembly which is bolted to the body which is grounded. I did not verify with a continuity test. Anyways, I grounded it and the light on the gauge cluster does not come on. I think I am going to take the gauge cluster and verify that power it getting through to the other end of the wiring harness.

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In better news: I fixed my low beam functionality by replacing the floor dimmer switch

 

[RustyPile]

Before you dig into the cluster, do the easy stuff first.. A simpler test can be done.. Disconnect the tan wire at the proportion valve.. Ground it to a suitable place.. The "brake" light on the cluster should come on.. This will determine that the bulb and cluster plug are intact. If it doesn't come on, remove and check the bulb, replace as necessary. If the light comes on, do the same thing at the parking brake switch.. If the light comes on, you have a problem with the parking brake switch.. If the light doesn't come on, you have an open circuit somewhere between the switch and splice point where the wire joins the main harness.

 

[legozombie]

So I tested the parking brake switch and it produced ground when it was supposed to just as our messiah and savior Paul Hitch intended to. When I tested the prop valve, the gauge side of the circuit was grounded (more than likely from the engaged parking switch) but the prop combo valve was not producing a ground. To be fair, my combo/prop valve looks like it's doesn't want to live anymore. Regardless of my prop valve's condition, I should be seeing a light on the gauge. As @RustyPile mentioned, There must be a disconnect between the ground points and the gauge cluster. I know the light bulb is new and I see a momentary bright light at the choke/brake indicators when I shut my car off (Possible oil pressure switch?). That must mean it's connection to the gauges or somewhere on that brown light. More to follow when I get more time.

Next troubleshooting step is to verify ground is getting to the harness. If it is, it is somehow not being received by the gauges.

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