I have an 89 F350 7.3L dually 2wd.

Borrowed a trailer from a friend a while back, and ever since my 20A brake fuse blows randomly and I have no brake lights (running lights fine). I am replacing the fuse every week it seems. I'm thinking the trailer had a bad ground, the plug on the trailer looked damaged at the time but it was an emergency situation and I had to use it.

Anyone else experience a similar issue? Do I need to replace the entire harness? Thanks!

 

welcome to FTE
if the trailer is not still connected that would not do it, unless the plug on the trailer was messed up and bent the pins in the trailer plug on the back of your truck shorting them out.

what i would do is disconnect the trailer plug on the back of the truck and see if it stops blowing fuses.

 

I was going to say it sounds like a chaffed wire inadvertently grounding out to the frame or body somewhere...

 

that very well could be to too Lee.

i like to start where the problem seemed to start and then work my way back to where there is no problem anymore.
disconnect trailer plug. if it stops that was the problem. if it is still there, disconnect at firewall plug. then at brake switch. sooner or later you will find a good spot and then can narrow down the area to investigate.