when I step on the brakes, it blows out the 20amp brake light fuse.
How do I trace wiring to find short.

 

Start by removing the bulb sockets from the taillight housings (that's how they're grounded) and see if the fuse still blows with the brake pedal. If nothing, reinstall one socket at a time and test again. You could have a short with one of the sockets, or the related wires, and isolating the lights may help tell you which one it is.

 

I just wanted to thank you and tell you what I found. It was a pinched brake light switch wire. Thanks Again.
Ray

 

Glad you found it, and thanks for reporting back with an update.