Trailer Lights
 

Does anybody know what that black box behind the panel behind the spare tire is for? It's in line with the trailer light harnes.
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It is called a tail lamp converter... It makes the trailer brake/turn lamps into a single circuit from the dual circuit in the jeep. the trailer does not have independent turn signals like your jeep so it would not work properly without it

sorry to hi jack but I didnt want to start a new thread since that guy just answered your question...My trailer lights dont work when hooked to my xj. They work fine on my dads truck but not mine. Where should I start lookin for the problem? I think it might be a aftermarket hitch and wiring cause it says u haul on the hitch...whatcha think?

No problem, it is on subject... You may want to start by checking the ground to the converter itself as it is usually grounded independently, next make sure that there is no fuse or power supply wire (most do not have this, but a few do) If you can not find any problems there, it is possible that the wiring could have been shorted out at some point and damaged the converter. I would HIGHLY suggest checking the ground first though as that is usually the most common cause of any electrical problem. Hope that helps you out.

I remover the converter, soldered the wires to an extension harness and installed a new 7 prong plug. Everything works fine. I just completely eliminated the converter but I checked it all out first. The striped red wire, I just sealed off with a piece of shrink tubing. I will not tow anything with my Jeep that is big enough to have to need tlr brakes.:)

this may sound stupid but what is a converter and where is it??? lol