my brother bought a trailer a few years ago and never ended up putting it together. I have all the parts and such but dont have the instructions to put it together.

I was looking at the light and it has two black wires and one red. i assumed the red was turn and the two black were the running lights and brake light wire. i took an old 4 pin wire set and started playing around with the light. i have tried every combination of wiring and i can get the running and turn signal to work but when ever i hit the brakes the whole light shuts off. any idea what i am doing wrong? do i need to have both lights hooked up for the brake light to work or what?

 

Trailer taillights typically have three wires coming from the lamp assembly. One wire for the running/park lights, one wire for turn/brake, and one wire to trailer frame ground.