I had that problem with mine. The tail lights would work, but the brake and signal wouldn't. Ended up replacing the converter and now everything works fine. Plug and play or universal shouldn't matter.

Have you checked the actual voltage at the lights for the brake/turn? And the voltage for the tails? Make sure it is at least 10V

 

Blinkers and Brake use the same filament on the trailer, make sure your bulbs are good. I've had both fail within hours of each other. Get a test light, probe on one end and alligator clip on the other and check your plug, if it's working there it's on the trailer somewhere. Also refresh your grounds!! A lot of older trailers use the ball as a ground. I've seen running lights work right after hooking up but brakes/blinkers didn't until I'd driven a few miles (rubbed the rust off the top of the ball/bottom of the coupler).

 

I have regrounded the trailer ground, the trailer lights work perfectly on my dads truck, and the trailers bout new so the lights are good

 

I thinks it's something to do with the trailer but I can't figure out what the heck it is.

 

Ok I used my test like all the way back to the bulb, it flashed when I punctured the wire for the blinker, but the light wouldn come on? Then all the sudden it blink about 5 times kinda dull, then stopped...them blinked again 5 times then stopped?
Could it be lack of volts?

 

As stated above, the blinkers and brakes on the XJ are two separate bulbs.....on the trailer, they are both in the same bulb, that's why the plug-n-play converter is needed.

 

Possibly low voltage. Use a meter to verify. I have LED tails on my XJ, wired to a converter. The first converter did the same thing you are describing. I swapped it for a new one and all is working as it should.

 

Ok no one was really clarifying exactly why I needed a plug and play. But now I know why

 

what kind of truck does your dad have? Are the brake lights and turn signals
the same bulb or different?
Also, run a temporary ground from your truck to the trailer, just to see if it is
a grounding problem.(you can use jumper cables for this)

 

2011 f 150

It is the same bulb for brake and blinker
Temporary ground? Not sure how to actually do that

 

It isn't needed, just makes it easier. I have used both with the same results in the end. If done properly, there is no difference. All the converter does, whether it be plug and play or universal, is convert the separate brake and turn into one bulb.

Again, I had my converter go out and produce the exact same problem that you are having. This converter was installed last year and I never used it until earlier this month. Low voltage output was the cause so I had to replace the converter.

Also, no mention of whether the trailer has LED lights or not. Make sure your flasher is set up for LED and can handle the extra bulb capacity. Get the LED 4-6 bulb flasher.

 

No led on trailer

I mean the converter is brand new I guess it could be a dud

 

Mine was a dud, straight from Orielly. Picked one up at AutoZone and it works just fine. And it is the exact same one too

 

Was the converter specific for your year XJ? We could not find a year/model converter locally for our XJ....ordered it from etrailer.com. It works perfect with the stock XJ flasher and the LED lights on our trailer. The correct/model year specific converter is fool-proof plug-n-play.