rackmaster2

2014 2500 diesel.
It seems I'm always having issues, it works, then it does not work., then it works again. I tried it on diff trailers , same thing. Ill be pulling a gn with a tractor and leave house and down the road, it will read service brakes.
sometimes, i unplugged and then replugged the connection and it would work, sometimes it does not.
I've checked all the wiring and connections in rear of truck , all are good, I have dia grease on each connection.
Sometimes it will blow a fuse in #19. but not always. ( trailer brakes)
not sure if related, but also it has blown fuse in #4.

I understand there is no good way to check to see if they work , unless a trailer is attached and it senses brakes. When I put a light to it, it usually will give one little dim light for just a second.
could it be a relay? should i replace ? any way to really check to see what the issue is.
appreciate it.