I think you should have 4or 5 wires? brakes, running lights, left signal, right signal and maybe a ground. If all your park/running lights dont work the problem will be near the front maybe at the connector or maybe a wire rubing on the trailer were it goes through the fram rail. use a test light and check the harness on the car/truck and find out witch wire does what and that each one has power (example white wire has power when the brakes on) If that turns up ok then the problem is in the trailer.