Trailer running lights

[Sierradad420]

I have a 2015 GMC Sierra and I had a light bar in the back for the brake lights connected to the 4 plug trailer light connector, one morning I started my truck up and the light bar was on working fine five minutes later I go out to my truck and the light bar was off so initially I check the fuses and all seem goodthe blinker lights and brake lights work fine for the trailer but the running lights don't work so I unplug the bar and tested each connector with a tester and found the running lights don't work at the plug. is there anything I can check before I start following wires? 

[Paintor]

Bet it happened after rain or carwash. Recheck your fuses. You will need a 20 amp micro fuse.

 

Plugs on harness along frame in front of rear bumper get wet and short. Dry them. Fill with dielectric grease inside.. and out. You are gonna break those little red tabs. Ignore them.