BP_MJ_978 Posted August 1, 2021 Share Posted August 1, 2021 Hi all, Looking for some help here, my Comanche currently has no brake lights, but all other running lights and the signal lights work. I believe the issue is electrical, but I am not sure how to diagnose further. My Comanche has a 96’ XJ brake booster and master cylinder swap with an adjustable proportioning value instead of the OEM brake switch. Unfortunately all of this work was done by previous owner, and I do not know much about electrical work. The connection at the prop block is good, but it is very difficult to follow the wire back into the dash. I’ve looked up wiring diagrams and pictures from other posts, but can’t find anything about how to wire this kind of set up. Does anyone have any info or pictures of how they did this wiring? Some other useful background, I recently removed both the lower and upper dash panels, as well as the instrument cluster to do another repair. When I put everything back I noticed two new loose wires, pictured below (one the casing is tan/yellow). Is it possible I disconnected an electrical connection somewhere that could be causing this? My speedometer and odometer also stopped working after I pulled the cluster, but all the other gauges still work. Could these issues be related? Any help or guidance would be greatly appreciated! Link to comment Share on other sites More sharing options...
87MJTIM Posted August 1, 2021 Share Posted August 1, 2021 There is the 88 Electric Manual in the DIY section. The booster and prop valve should not have affected the brake lights. Link to comment Share on other sites More sharing options...
Pete M Posted August 1, 2021 Share Posted August 1, 2021 do you have a multimeter? check for power at the brake light switch, then for continuity through the switch when activated. the speedo/odo are cable driven. it's possible the cable didn't get clipped on tight enough when you re-installed it. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 2, 2021 Share Posted August 2, 2021 The brake light switch is located where the pedal attaches to the booster. That wire on the proportioning valve is for a brake warning light on the dash if there is a pressure failure in the brake system. Link to comment Share on other sites More sharing options...
mjeff87 Posted August 2, 2021 Share Posted August 2, 2021 Do your dash/instrument cluster lights work? The brake lights are mysteriously wired into the dash lighting circuit.......the engineers of the day designed it that way so as to let you know if your brake lights go out. Since you (normally) can't see your brake lights not working, the dash lights cut out to give you a warning. Check the 5 amp "INST PNL" (or something like that) fuse to see if it's popped, or loose. Could be as simple as that. edit: post #3 in this thread shows a good shot of the fuse block. Check the 5A fuse at the bottom right of the block (picture is rotated). Link to comment Share on other sites More sharing options...
BP_MJ_978 Posted August 5, 2021 Author Share Posted August 5, 2021 Thanks everyone for all info. Unfortunately the previous owner seems to have been a self-taught electrician. The wiring diagram does not match what’s in my Jeep and I do not have a brake light switch on my pedal, see pictures. I do not appear to have to dash/cluster lights, so I tried the replacing the fuse, but no luck there either. To make matters worse, now my turn signals do not work either, but the hazards still work. I’m not sure where to go from here, does anyone have any other ideas? Thanks in advance! Link to comment Share on other sites More sharing options...
jdog Posted August 5, 2021 Share Posted August 5, 2021 Why do I Have a feeling that the loose wires in the first picture were just plugged into random fuse slots Link to comment Share on other sites More sharing options...
BP_MJ_978 Posted August 5, 2021 Author Share Posted August 5, 2021 jdog, that would make sense based on the length and possible places the wires could reach/plug into. Unfortunately I don’t have any pictures of me fuse box to reference. Is that something you’ve seen before? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 5, 2021 Share Posted August 5, 2021 Link to comment Share on other sites More sharing options...
jdog Posted August 5, 2021 Share Posted August 5, 2021 1 hour ago, BP_MJ_978 said: jdog, that would make sense based on the length and possible places the wires could reach/plug into. Unfortunately I don’t have any pictures of me fuse box to reference. Is that something you’ve seen before? Yeah, it would fit the bill, especially since I Have your fuse box has had brake fluid from the clutch on it and caused the terminal to not grip the fuses. It also looks like there are fuse holders in line in the wiring harness Link to comment Share on other sites More sharing options...
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