taillights problem

ok......here it is,almost spring,gonna dig my truck out of the snow.........and fix my taillights!!!!! its kinda complexed ,but here it goes....thanx in advance.....

i have a 92 gmc sierra with shaved taillights.last summer i just ran 2 (1 on each side)oval transport trailer lights(12V).worked great for about 2 months.i wired them as though i was just simply pulling a trailer behind my truck and unplugged my stock taillights and took them off.then,one day,all of a sudden i started blowing bulbs in the trailer lights.....tried to hook up the stock lights again and everything works good........i wanna get 2 led strips but first i gotta figure out this problem