Not too likely on this truck, but does it have trailer wiring? Many times that's the best place to start.
After that, use a circuit breaker in place of the fuse and disconnect circuits until you find the area that's popping it. It would help to have a factory wiring diagram, but can be done without.
I will probably have to start there. No trailer wireing.. this was his 98 year old grandmas truck until a year ago... she has had it forever to get groceries...
