The trailer brake and left turn signal lights stopped working so I checked the fuses after completely wiring the trailer and found a blown fuse. I found that each side of the trailer has it's own fuse which controls the brake and signal light. I replaced the left side which was blown and now the turn signal works but the brake lights still don't work. It's not the trailer wiring because everything works fine when hooked up to my old truck. Any suggestions?

 

What F150 do you have, do you have four pin or seven pin harness, where were the fuses located?

 

Get a meter or test light and check that the plug on the truck has juice going to it first. Then try to go from there. Electrical problems can be a pain to find. This would be the first thing I would check.