If your lamps only have 2 wires they are internaly grounded. The ground is made when they are bolted to the trailer frame. Something that is often overlooked on old tilt trailers is that the coupler part of the frame does not have a positive ground conection with the rear tilt portion and they need a jumper wire installed to make a good ground between the 2 parts. Just a little something to think about.but the lights only have 2 wires, brown/yello, and brown/green, coming out of them. How are they grounded?