1996 c1500 brake lights .......please help!!!!!!!!

my brake lights went out on my 1996 c1500 all my other lights work except for some reason i cant get the right side turn signal bulb to stay in. i have bought a new circuit board and still have that problem. checked my brake switch....good.... all wires under the truck are bundled up look like they are in good condition. please help i need to get this working so i can hook up my trailer for my boat but i got to get this problem fixed before i hook that up. oh one more thing. none of this was going on until i tried to hook up a connector for my trailer lights on the truck. i have 5 wires under the truck that are hanging bare if that helps. they are yellow, light green, dark green, a big white one and a big black one, those are both connected to the frame like a ground or something.....please help me....