I have a 5x10 trailer, it's 1 year old, bought new. The driver's side trailer light stopped working. I replaced the bulb, yet still no go. I went to Northern Tool and purchased a new entire light and installed it. It still will not work. I checked the ground and wires, none appear broken. Passenger side trailer light works great. I have a 2004 Ford F150 4x4 with the round and straight plug, currently using the straight plug, which according to my volt meter is getting power. Should I buy an adapter for the round plug and give that a try or replace on the hitch wiring in the truck???