1997 Chevy Blazer LT 4x4 blowing stop light fuse?

Everything was fine until the day before yesterday. Now every time I step on the brakes the 20amp fuse for the stop lights blows. Only thing I did different was took neighbors boat to the lake and everything was working fine when we went up but quit working on the way back. Also the dome light will come on on its own since this happened. I have towed many trailers with it before and never had a problem. Have replaced the trailer light wiring harness and the stop light bulbs and didnt help. I know I have to have a short somewhere but don't know where to start looking. Thanks