Hi, I have a 1997 cherokee and the trailer brake lights aren't working. I went to rent a uhaul and when we tested, only the right lit up. The lights on the trailer corresponded. I checked the fuses under the hood and took apart the driver rear quarter panel and nothing is obviously wrong. No corrosion, frayed wires, etc... I haven't checked everything with a multimeter or farther than the quarter panel, but is there anything else I should know or try? (I have an after market stereo system where the wiring runs in a lot of the same places that could have possibly been messed with when I installed it)

 

Assuming that this is an after market wiring loom from the vehicle to the trailer. Somewhere under the carpet or tucked behind the plastic sidewalls in the cargo space or maybe even hanging down under the back bumper, you will find a little black box with wiers giong in abd coming out. That is your wiring converter. Start testing there. See if power is coming in for each terminal. Brown should be a ground wire. If it is coming in, see if it is going out. If it is not coming in, start tracing the wires. If its in but not out, the converter is bad, but that is rare. If it is in and going out, trace wires to your plug. Cheap plugs are notorious for going bad from corrosion.

The two biggest problems with trailer wiring is always bad grounds and or bad/ corroded/ broken wire splices. A bad ground can really make trailer lights act strange.

 

Take a multimeter to the plug on the xj and check there first on all pins. Layouts available online because depends on number/country etc.