I had my ford escape wired for a trailer. I put a new set of lights on my little dude trailer. (each light has a big and smaller side bulb)
• When I step on the brakes all four lights go on ( two on the left and right)
• when I put on the left signal - both lights blink in the left light, but both lights blink weakly in the right light also
• when I put on the right turn signal just the big bulb blinks in the right light

If I put on the running lights or headlights in the car:

• all four lights go on
• when the left turn signal is on - both lights in the left light work!
• when the right turn signal is on - just the big bulb in the right light goes on

help!!!!!! please

cb, August 2009

Sounds like you have no earth return wire from trailer lights back to the car chassis, and/or a poor connection in the earth return path from the trailer light bulb to car chassis. When the indicator is trying to work, the only path back to earth on the car is through the filaments of the other lamps.
Check that there is an earth connection from the trailer plug on the car back to the car chassis, it is not enough to rely on the body of the plug and the mounting bolts you must install a wire from the earth pin on the trailer plug to a lug and bolt to the car chassis. Next, check there is an earth connection in the trailer plug, that connects to the earth on the trailer lights.

trover, August 2009