Have a ford f900 dump truck. over the years some times the marker lights on the dump box go out, not the cab only the box. I have changed out the light switch in the cab, no difference in results. Today I finished painting the dump box and put the marker lights back in the box with the lights on during this time. When all lights were installed and they all worked, I turned off the light switch. The I turned it on to see if they would light up, NO LIGHTS. Just like that lights on moment and the next no lights. What in the world could be wrong. Any suggestions would be greatly appreciated.
Have you checked to see if you have voltage at any of the lights?? Make sure you have a good ground on your meter or light, then check all light plugs. If no power at any of them, you're going to have to trace the wiring back to the source. If you have power at the lights, you need to investigate the ground.
Since it's only on the box, I would think the problem is lack of ground. Run a ground strap from the box to the frame somewhere, to metal sanded clean and shiny, bolted solid. Then make sure the marker light ground wired or the harness wire is grounded to the box properly as well. We used to have dump boxes the marker lights would only work when loaded, had enough weight to make the connection at the pivot pins.
Have you seen some of the cobbled rear light wiring on dump trucks? I can't believe it sometimes. A trailer box that's sealed with new light cord would be a start. Glue it on the frame with silicone caulk. Now you can test your wiring easily. Since I have been doing this light problems are a thing of the past.
I am going to try this.
Also make sure the wiring isn't pinched at the pivot point.
Might be worth a look in the junction box.
Agree, some people get lazy about running a jumper from dump body to the main frame of truck or trailer. If one light goes out check that one, but if all go out it is most definitely a ground problem. As a quick test when lights are not working try hooking a set of jumper cables from box to truck frame.