I have no rear tail lights in my 03 envoy slt. Fuse keeps blowing

So I have rear break lights, reverse lights, blinkers, and head lights, but no rear
running lights. There is power at the fuse box and the circut board is good. It
calls for a 10a fuse, and it blows immediately. I tried a 20a and a 30 and same
thing happens. My power windows work, my radio, and all the controls. But no
dash lights. The circut breaker under the hood is good.