This is a wiring question on my trailer.

I have a 6' x 9' trailer. I rewired just recently. Here is the problem: The right-hand side works perfectly. Brake, turn and running light works just fine. The left-hand side doesn't work at all. I put my test light on the wires and it runs my test light just fine. When the running lights are on my test light, lights up. When I hit the brakes, it comes on as well. Hit the left-hand turn signal, the test light blinks. When I hook up the actual trailer light, it doesn't work. I have the light fixture bolted to the frame, I can use my test light and poke inside the fixture and it works perfectly. I install the bulb, it doesn't work. I tried 6 different bulbs and the same thing. I am at a loss, I have no idea? I made sure the springs in the light fixture are touching the bulb, and still nothing?