Lights intermittently cutting off on Freightliner Coronado

Has anyone ever experienced their headlights and all their marker lights going out on their truck or specifically a Freightliner Coronado? It happens randomly and there seems to be no specific pattern to it. I have never had this issue when bobtailling. It always happens when a trailer is hooked to the truck. I also loose running lights on the trailer when this problem occurs. I still have turn signals and brake lights, on the truck and trailer. The issue could last a few hours or a handful of hours and the lights will come back on. I will list the things that I have tried/replaced below. Any help would be greatly appreciated! Thanks!

1. Changed headlights to LEDs with resistors built in, thinking that the LED headlights without resistors could be the issue.
2. Cleaned out connector from chassis harness to left headlight harness (it was very dirty), put new seal in connector
3. Changed out switch in dash
4. Changed out headlight breakers
5. Changed out headlight relays
6. Changed out trailer relays
7. Changed out 7 way
8. Changed out abs cord
9. Changed out 7 way harness cord that runs under the truck to the main chassis harness
10. Replaced taillights
11. Replaced taillight harness

 

No Sir. I believe everything else functions as it should.

 

I will definitely look into this. Thanks for the info!