This,

like I said, the truck plug has one to the truck frame and same with trailer, from trailer plug to trailer frame. The lights are also grounded to the frame of the trailer.

Well we're up and running I replaced both the back tail lights and as long as I had the jumper wire from the batt. connected they worked fine but when I disconnected from the batt. it started doing all sorts of thing so I connected a heavy jumper from the rear hitch on the P/U to a bolt on the trailer hitch and every thing works like a charm, so definitely was a grounding problem and apparently with what rust and crud that I can't get out is enough to affect the lights. Once again thanks to all the people with all the comments and suggestions it was much appreciated.

Still fishing? Make hay while the sun shines!!! This weekend is spose to be warm again.

99% of the time trailer light problem is a bad ground. Old style lights with the 1157 bulbs the socket gets corroded and the bulb wont ground. Unplugging the trailer before you back in the water helps save the bulb but that socket corrodes and every year or two you need new lights. Sand paper is a very poor fix. Dont last long. Ground through the ball hitch everything works for awhile when its all new. With a receiver hitch ball its even iffier. I quit using the trailer frame a long time ago for a ground and ran a wire all the way back and connected both lights to it. If I wire in the vehicle plug (have not had to in quite a long time) I run a wire all the way to the - battery post. Yes you can ground to the frame or something but never had any problems from a wire to the battery. Solder and shrink tubing. Cant say that enough. With led trailer lights no more ground problems from bad sockets. Its real nice to hook up to your trailer after it sat a few months, plug in the lights, and they all work properly.

Every boat I ever owned had aground wire from the plug directly to the light. NEVER had an issue with a ground. Too many spot and points of ground to be painted or rust to rely on the frame for the ground. First one I bought was a new stratos 17 ft in 1986. Why would anyone even try to use the frame. The vehicle plug has a ground on it .IF it doesn't theyre only 5 bucks on amazon with 60 in wires......