I've searched this topic but not getting what I need. We added a curt trailer hitch and plug in wiring harness to our 99 XJ. It all went together easy enough but when I plug the trailer in the only thing that works is the tail lights. I've got no turn or brake lights. The trailer is fine as I hooked it up to another vehicle and everything works. I've got power for each function (test light) at the plug but once I plug the trailer in, I get no turn or brake at the back of the trailer. I've also verified I've got wires matched up on the plugs. Any thoughts on where to start diagnosing this? Wondering if the converter is bad as I read happens but it works at the back of the Jeep so I'm not sure. Thanks!

 

Does the trailer have separate brake lights & turn signals?

 

No, it does not.

 

Any update on this? Having the same exact issue.

 

Did your plugin harness have a black box as part of it? You XJ has separate turn signal lights from the brake/running lights. The black box converts these inputs to make the trailer lights function. Trailers do not have separate turn signal lights.

If you don't have the black box you have the wrong wiring harness for your vehicle. If you have the black box then it's probably bad. I've had them fail similarly. The running light are straight through, but turn and brake signals have to go through the black box circuitry.

 

It did have the black box, It was a curt plug and play that I ordered from Amazon. Ended up ordering a Hopkins and everything works perfect now. The one I got from curt must have been defective.

 

Can you link the part you got? We have the factory towing package and recently our trailer lights act like you described.

 

https://a.co/d/2haJj2a It only took about 5 minutes to install.