2015 freightliner m2. IT IS NOT THE TRAILER, truck does it with multiple trailers. No trailer, all lights work fine. Key on or engine on with trailer, key on, lights on, everything is fine With trailer engine on, marker lights shut off after a few seconds. Restart truck lights come back but turn off again any suggestions
First try a new or known good light cord. If nothing changes I would then check the receptacle wiring (what the cord plugs into) on the tractor and make sure all the connections are clean and tight.
All connections are good at the 7 way, even tried removing it from the truck so it doesn’t short to ground and still nothing
Does it have the relays behind drivers seat? Maybe a weak relay that’s not holding contact with the truck running?
Sounds like a marker light relay in the circuit breaker / fuse box or the light switch on the dash is getting overloaded and intermittently cutting off. The switch may seem fine on the outside but the contacts inside go bad from years of heat and load on them. They can work fine until you add the extra load on them from the trailer lights then it makes them wig out.
