[patrickt]

Bench testing that little baby is quite difficult, as it has to be under load. First confirm that the bulbs on all four corners are not burned out on either of the filaments in the bulbs and that they are making a good connection. You do this by manually feeding 12v+, using a needle on each feed wire, to test each filament to visually confirm that the lights come on with both of the filaments. Once you know all filaments illuminate properly, you then work your way backwards to the trailer relay.