Eagle_SX4 Posted June 9 Share Posted June 9 Recently I noticed my back up lights are not working. I have tested the switch on the transmission and it functions properly. There is voltage getting to the switch. I don't have voltage at the reverse bulbs. The brake lights and turn signals work fine. One odd thing is that when I pulled the right rear tail light out it is clear someone has done something with the ground there as is was cut and spliced back together. Which fell apart when I pulled the light out. Crazy thing is my fuel pump still runs even with that ground disconnected. I don't think that should happen. I got a NOS wire diagram off eBay for the 87 Comanche. The problem is the reverse light circuit is not included in the diagrams. The index says it should be at location W-6 but that location has the power seat diagram. I also have a 91 service manual but the diagram for that is only applicable to the Cherokee. Does anyone have a diagram for the reverse lights? Link to comment Share on other sites More sharing options...
eaglescout526 Posted June 9 Share Posted June 9 Wild thought. Is the trans fuse blown? I have no idea if the fuse affects power going to or from the switch though. Link to comment Share on other sites More sharing options...
Pete M Posted June 9 Share Posted June 9 corrosion in the rear harness connector can cause this. check for power there. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 9 Author Share Posted June 9 12 minutes ago, Pete M said: corrosion in the rear harness connector can cause this. check for power there. Check the connection and it was like new inside with no corrosion. 40 minutes ago, eaglescout526 said: Wild thought. Is the trans fuse blown? I have no idea if the fuse affects power going to or from the switch though. The fuse tested good but I swapped it out any way and it my lights are working now. Still strange that there was power at the switch but they still didn't work until I changed the good fuse with another good fuse. I must have corrosion in my fuse block. I have new terminals to rebuild the fuse block but have been putting it off. That will be the next project I need to tackle. Thanks for the help. Link to comment Share on other sites More sharing options...
eaglescout526 Posted June 9 Share Posted June 9 No problem! How are the contacts on the fuse itself? I know lately I have been battling corroded fuse legs on my XJ and barely supplying 12v to what its powering. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 9 Author Share Posted June 9 The fuse looks new and tests good. Not sure what happened but I do have one fuse slot that only has 1 side of the prong due to corrosion from the previously leaking clutch master. Not looking forward to pulling the fuse block and repairing it, however it needs to get done. Link to comment Share on other sites More sharing options...
Pete M Posted June 9 Share Posted June 9 was there power at the connector? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 9 Author Share Posted June 9 10 minutes ago, Pete M said: was there power at the connector? There was not power at the connector by the tail lights but there was power at the connector for the switch on the transmission. I changed the fuse and everything is good now. Link to comment Share on other sites More sharing options...
Ωhm Posted June 10 Share Posted June 10 4 hours ago, Eagle_SX4 said: Crazy thing is my fuel pump still runs even with that ground disconnected. I don't think that should happen. If you or someone else performed Cruisers Tip #29 (Fuel Pump Grounding), then pump will continue to RUN when ON. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 10 Author Share Posted June 10 2 hours ago, Ωhm said: If you or someone else performed Cruisers Tip #29 (Fuel Pump Grounding), then pump will continue to RUN when ON. I did look for an additional ground along the harness but could not see any. It must be hidden behind the gas tank. I am fairly certain the tank has been replaced before. Link to comment Share on other sites More sharing options...
schardein Posted June 11 Share Posted June 11 If the problem recurs, you can use this picture to test for voltage at the tail light harness connector. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 12 Author Share Posted June 12 On 6/10/2024 at 6:18 PM, schardein said: If the problem recurs, you can use this picture to test for voltage at the tail light harness connector. Thanks. The thing I don't understand is that I had voltage at the transmission switch but not at the connector until I changed the fuse. I would like to understand why. Does anyone have a schematic for the rear lights? Link to comment Share on other sites More sharing options...
JYau Posted June 14 Share Posted June 14 The 88 electrical manual shows the backup lights wiring, does this help? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 14 Author Share Posted June 14 1 hour ago, JYau said: The 88 electrical manual shows the backup lights wiring, does this help? That looks like the correct schematic but I can't read it the resolution is to low. Is there any way you can upload a higher resolution? Maybe a PDF file? Link to comment Share on other sites More sharing options...
Ωhm Posted June 14 Share Posted June 14 _mj1988electricalmanual_1.pdf Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted June 15 Author Share Posted June 15 Thanks @Ωhm. They must have altered something from 87 to 88. The plug at my transmission (originaly a BA10/5 swapped to an AX15) is a 4 slot weather pack connector with 2 of the 4 looped and it doesn't show that on the schematic. The only mods the previous owner did to the harness was cut off the puegeot switch and connect the new AX15 switch to the old wires. However I think Jeep changed to a separate manual transmission wire harness in 88 because I have the square plug for the auto transmission tps sitting unused by the throttle body. My truck has always had a manual transmission according to the vin. Link to comment Share on other sites More sharing options...
gogmorgo Posted June 15 Share Posted June 15 How are you checking for voltage? Voltmeters can trick you. They detect voltage with a tiny amount of current that might make it through a poor connection at the fuse, but that isn’t enough to push its way through resistance in the rest of the circuit. Using a test device like a test light that loads the circuit even just a little is usually enough to prevent tricky readings like this. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now