Timeless Posted November 4, 2014 Posted November 4, 2014 I'm trying to finish up my build and my MJ keeps resisting...87, 4.0L, AW4 btw. After bleeding my brakes and reconnecting my battery I realized that my brake lights, the ones in the back of the vehicle, (not dash indicator if one even exists) are always on if the ignition is on/truck is running. There is no change if I push down on the pedal, pull up, wiggle it around. I'm not sure if this means the switch on the brake pedal is shot but my best guess is that the problem was somehow caused by pumping the pedal during brake bleed. I have temporarily disconnected the switch on the brake pedal (no, I'm not driving the rig around). Has anyone had a similar issue? If so, what was the resolution?
HOrnbrod Posted November 4, 2014 Posted November 4, 2014 Press the switch detent button with your ohmmeter hooked across the brake light wire terminals, ignition off. Observe meter for continuity in one position, open in the other.
Timeless Posted November 4, 2014 Author Posted November 4, 2014 Yes, I have a multimeter. The switch on the brake pedal does not appear to move at all. I'm kind of thinking I somehow jammed it up while bleeding the brakes, but I really don't even know how exactly it is supposed to operate. I can check continuity to verify the brake pedal switch is in fact the problem, but based off all the other symptons and the fact that if I disconnect the switch the lights go off, I'm thinking it must be the problem. Thanks for the feedback thus far!
HOrnbrod Posted November 4, 2014 Posted November 4, 2014 It's a switch, makes and breaks when you push in the brake pedal. If it doesn't, it's broke and needs replacement. This is the one you need (if you don't have cruise control). http://www.quadratec.com/products/55217_04.htm With cruise control: http://www.quadratec.com/products/55217_03.htm
mvusse Posted November 4, 2014 Posted November 4, 2014 What puzzles me is the ignition. The brake lights should work no matter the ignition, or a key even being in it. Just like most of the rest of the lights. The only lights that should only work with the ignition being on are turn signals (but not hazards flashers) and backup lights.
fiatslug87 Posted November 4, 2014 Posted November 4, 2014 My 88, 89 and 90 do not have cruise control but the switch is the flat one shown for "with cruise control" in hornbrod's quadratec links. The round one looks like the one for the SJ. Here is the FSM instructions, if you do not have it, showing orientation of the switch & associated spacers/bushings.
Old man with MJ Posted November 4, 2014 Posted November 4, 2014 The part no for the Mopar one is 1-J3215938
sloride Posted November 4, 2014 Posted November 4, 2014 mvusse, If memory serves, I'm pretty sure the ignition has to be on for the brakes to light. Its the same with the horn. At least its been that way for mine since I drove it off the lot new. Before I test drove an MJ for the first time back in '87, I tried honking the horn without the key in the ignition, like any other vehicle I've driven, only to have the sales person tell me to turn the ignition on first.
mvusse Posted November 4, 2014 Posted November 4, 2014 Just tried both my 87s. You are correct about the horn, I never realized this until now, but on both the brake lights work fine with the ignition off.
sloride Posted November 4, 2014 Posted November 4, 2014 Well, cr@p! I'm getting old and forgetting stuff then. I'd have bet money. I'll check my lights first thing when I get home.
HOrnbrod Posted November 4, 2014 Posted November 4, 2014 You got me curious too - just checked the 91. The horn blows and all the lights work with the ignition OFF.
Timeless Posted November 4, 2014 Author Posted November 4, 2014 The brake lights stay on with the ignition off on my rig too. Between disconnecting/reconnecting the battery and messing with the switch, I didn't notice originally. Hornbrod, the brake switch looks similar to the flat one you linked over. Thank you. I know for sure the switch is not round. (Edit: looks like quadratec just has the wrong stock image.) Seeing as this thing is possibly just jammed (hopefully), I'm going to try to remove it and free it up and get a replacement as a backup. I need this rig done by the weekend and its getting tight!
Timeless Posted November 4, 2014 Author Posted November 4, 2014 My 88, 89 and 90 do not have cruise control but the switch is the flat one shown for "with cruise control" in hornbrod's quadratec links. The round one looks like the one for the SJ. Here is the FSM instructions, if you do not have it, showing orientation of the switch & associated spacers/bushings. Awesome! Atleast I'll be able to put this thing back together correctly.
fiatslug87 Posted November 4, 2014 Posted November 4, 2014 Any parts store will have the switch for less than $10, don't bother trying to unstick the old one. Just replace it, you don't want to do it twice.
sloride Posted November 5, 2014 Posted November 5, 2014 Sure enough, my brake lights work without key in ignition too.
Timeless Posted November 29, 2014 Author Posted November 29, 2014 To hopefully conclude this thread...the problem is not the switch but rather how the switch is oriented on the brake booster rod. The PO installed hydroboost from an astro van and modded the brake rod to work with the comanche brake switch. For some reason unbeknownst to me the switch has decided its not happy with this anymore. So, in conclusion, we all learned that brake lights work even when the truck is off. :D There is more to this brake saga to be continued in another thread.
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