Rob82

hey guys so I have found another issue thats got me stumped. 99 grand cherokee factory trailer light harness is acting funny, there is no sign of tampering with the harness at all from the connector up to where it enters the unibody. it has the 7 pin connector and i have a 7 to 4 adapter the issue im having is all lights work as they should when the head light switch is in the off position when the head light is in park light or head light mode i loose all lighting; marker, stop, and turn on the trailer the jeep works fine. i have plugged my adapter into my brand new pick up truck and also hooked the trailer's 4 pin direct into the truck and both work properly so i know the issue is with the jeep but cant seem to figure it out anyone run into this or have some idea on whats causing this i need the lights to work so i can tow in two weeks

Rob82

Hey found the issue incase anyone runs into this same problem on the factory installed trailer lights the pig tail that runs from the hitch up the left side into the unibody, if you remove the left rear interior panel in the very back of the jeep you will see where the harness comes up from the floor and runs into a pocket in the body inside that pocket there are three relays which I'm guessing act like the converter needed to go from separate turn and stop bulbs like on the jeep to shared like on the trailer anyhoo from the relays the harness runs into in my case a green connector into the main harness for the rear lighting. I had a bad relay, replaced it and the trailer lights are all working as they should. I hope this info can help someone else down the road.

dave1123

It's good you posted your fix. It will help others. I was going to suggest the problem was with the trailer lighting module and I see I was correct. My neighbor had the same problem with his Wrangler and his fix was to run turn signals on his trailer and eliminate the module. This caused the signals to flash too quickly, but he didn't care. He says he will go with LED bulbs on his trailer. IDK because I haven't talked to him in over a year. He's out of town so much we seldom see each other.