7tonemonte Posted July 4, 2021 Share Posted July 4, 2021 What are the common causes for the interior brake light to be on? Brake fluid is full, Park brake is released and plunger is fully depressed. Don’t see any wiring off of proportioning valve or e-brake It just started at Carlisle, and it does dim slightly, but can’t figure it out. I know someone here can point me in the right direction Thanks as always Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 4, 2021 Share Posted July 4, 2021 Those are the only 2 points that should trigger that light. If you don't see any wires going to either switch, somewhere there's a short to ground. Maybe those tan wires are hidden somewhere and finally rubbed against something metal to complete the circuit? That's my first guess, without getting into deeper issues like dash circuit board, or wiring harness faults. Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 4, 2021 Author Share Posted July 4, 2021 23 minutes ago, jft69z said: Those are the only 2 points that should trigger that light. If you don't see any wires going to either switch, somewhere there's a short to ground. Maybe those tan wires are hidden somewhere and finally rubbed against something metal to complete the circuit? That's my first guess, without getting into deeper issues like dash circuit board, or wiring harness faults. Kind of what I thought with only a couple reasons. It is bugging me and I keep them there is an issue now Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 4, 2021 Author Share Posted July 4, 2021 Ok so if I unplug it from propertioning valve light goes out. Is this telling me there’s an issue with the valve? Quote Link to comment Share on other sites More sharing options...
Dtret Posted July 4, 2021 Share Posted July 4, 2021 It’s possible that there is crud built up in the valve not letting is move to full open or closed position. Not really sure how they work but something has to slide in there Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 4, 2021 Share Posted July 4, 2021 So initially, you said there were NO wires going to either the prop valve, or the e-brake switch (located right on the park brake assembly). If you do actually have a wire to the prop valve, and the internal switch is made up, then yes, something in the prop valve is causing it to ground and light up the dash indicator. Usually it will light when you lose either the front or rear brakes due to a burst line or something like that. The internal contact will slide over to make the light work. If you bleed the brakes, it can sometimes cause it to make up too, but not usually. Has either of those things happened recently Tony? Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 4, 2021 Author Share Posted July 4, 2021 I meant there were no wires disconnected. I Have not lost any brakes, or bled any. the rakes all seem totally fine, stopping the same as always. I haven’t taken it out and stood on it to see if all 4 are locking up but it does seem normal. Basically everything was replaced except for the proportioning valve about 15 years ago. I know, should have done it then it seems as if I probably need to replace the valve at this point Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 4, 2021 Share Posted July 4, 2021 After re-reading it, now I see what you mean about the wiring or lack of.. (hey, I went to public schools, lol). You can pop the top off those valves (where the wire attaches) and center the switch too. Another way is to try bleeding the brakes, to get it to shift, depending on if it's stuck front or rear (probably better, so you don't get brake fluid everywhere, then have to bleed it anyways...actually, if the internal seals are good, no brake fluid should come out that switch port.). If you've never touched it though, it may just be corroded or bad. They make a little tool for that everyone is trying to sell now for when you bleed the brakes to keep that switch centered. I never needed one before, so I don't own one now, lol. May be worth looking into it, just for grins. https://techtalk.mpbrakes.com/proportioning-valve-bleeding-tool EDIT: this shows you just about everything you wanted to know about prop valves. That tool I mentioned is at around the 2:57 mark. Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 4, 2021 Author Share Posted July 4, 2021 Thanks for that Joe. Definitely something I’ll need to do 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 4, 2021 Share Posted July 4, 2021 Keep us updated if you get it resolved. Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 5, 2021 Author Share Posted July 5, 2021 Would this light just trip without me messing with brakes or bleeding or anything? I suppose the valve could just go bad and trip the light,? No leaks anywhere that I can see, I’ll try to hit a parking lot tomorrow and see if all 4 wheels are applying pressure Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 5, 2021 Share Posted July 5, 2021 Something is grounding the circuit to trip the light. Could be either brake prop valve, park brake switch, wiring harness issue, or circuit board issue (least likely cause?). You said pulling the prop valve wire extinguished the light, seems that's the issue. You could hook an ohmmeter to that switch contact and ground, but seems redundant. Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted July 5, 2021 Author Share Posted July 5, 2021 I hooked a test light to positive terminal and probed switch, light came on which would indicate bad switch. As the switch is just basically a ground. Then the test light went out, and when I plugged wire back in dash light went out. I did order a switch from Right Stuff, if it comes back on I will replace the switch. I was glad that was replaceable without doing the whole block. Thanks for the help, I will post any updates as soon as I get the new part. not sure why the light went out now, but I’ll keep an eye on it. Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 5, 2021 Share Posted July 5, 2021 Did you order just the part where the wire hooks to? That's basically just a contact pin, but the sliding part inside the block itself is what moves around and grounds the circuit. Is your prop valve the old cast iron type or the newer brass one? If the cast type, I could maybe see rust/crap in there possibly shorting it out? Just a thought. Quote Link to comment Share on other sites More sharing options...
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