The year of the truck would be helpful. Lots of wiring changed through the years for rear end lighting.

If everything was lost suddenly, there is one, and possibly 2 grounds at the back of the truck that all the taillights/brake/turn & license plate lights use. I'd start looking for a bad ground. The 70s trucks grounded the tail lights through the screws that hold the light fixture to the body. A bit of rust on the screws, or the sheet metal the \screws go through means poor lighting. By the mid 80s, Dodge added 1 ground wire foe the entire rear lighting, then a few years later, added a second ground. the 2000+ trucks have several grounds, and may also have the lighting ran through a lighting computer. Good luck with those.

I usually grind a clean place at an easily accessible location on the frame (grind clean both surfaces of the frame at that location), then I will drill a 1/4" hole through the frame and install a 1/4" x 1" long bolt with flat washers on both sides, and a nut and tighten the bolt to the frame. Then I will add a specific ground for each light and connect them to the bolt with 1/4" eyelets. Then add a second nut to secure all the wire eyelets to that bolt. 4-5 years later, then everything starts getting crusty, just reclean the frame and replace the bolt and whatever eyelets need to be replaced.

The next question is, does the fuel gauge still work? Gene