Here in Northwest Washington many small boat owners who frequent the Salt Water launches of Juan de Fuca Strait utilize a simple and "Permanet" cure for the various light problems being disscussed in this thread. The lights are removed from the trailer and attached to a length of wood or light metal bar (I use a wooden 2"x2") the lights can then be attached and removed from the trailer before and after launching and retreival of the boat. Obviously they still need to be connected to the tow vehicle with conventional plug in and ground wire! An added bonus to this is it will work on any other small utility trailer that you may own or have cause to borrow. Not to mention any names but some brave souls own several trailers and put one traler license on the bar and use it for all there trailers.