Trailer lights inop at times, a common problem?

[SVO1]

I tried searching but did not find this
. I have a freind with a 97 Ex that has an issue that when he hooks his trailer up, the lights will not work. If it sits for a while, they will just suddenly start working.
He has the factory Trailer package/ford trailer wiring.

I can hook it up to my 97 Mounty and it works fine.
Is there a controller/convertor that normally fails?

 

[NOTAJP]

A lot of the times it's due to faulty ground. The trailer grounds itself to the vechicle via the trailer hitch. Try running a wire with a clip or something from the frame to the trailer frame. Check all the grounds on the wire harness, also coroded connections.

 

[Alec]

Yup, most likely a grouding problem. You just need to connect the 2 vehicles with a separate wire.

 

[Crankcase]

Does he have a chrome ball, or a painted one? The ground could be at fault, or his trailer relays are on the way out.....

 

[SVO1]

He has a chrome ball, and an under bumper reciever.

 

[anchored]

I had the same problem with my factory wiring harness, so I just bypassed it and wired directly to my lights. Still, you can't overlook that the problem could be the lights on the trailer, especially if it's a boat trailer - they seem to malfunction all the time.

 

[SVO1]

I will check the ground. The trailer he is towing is my car trailer, and it has all new wiring/lights, and it has no problems behind my Mounty, Or my Suburban.
Just his truck.

It is so odd.. you can hook it up at night, and they do not work. Do not touch or move the Ex/trailer, come out the next morning and they work just fine.
Almost like a breaker re-setting itself or something.