Drove in the rain last night and parked the truck. Went back in it and put the headlights on and the gauge lights didn't come on. tail lights and marker lights don't work, only brake lights. Disconnected the tail light connectors and removed the turn signal bulbs but the fuse blows as soon as I turn the headlights on. what could be wrong

 

Got a trailer harness on that? Start there.

 

The wires to it were cut awhile ago...also replaced headlamp switch to no avail

 

Is yours spliced in, or is there a connector?

 

Did some driving around today and put the fuse in at the end of the day and it worked. But would still like to know what is getting wet. The harness was installed like a couple years ago. I think it's spliced in.

 

I would have a look at those splices then. Even the factory trailer harness is problematic.