Add a ground wire to your light socket and ground it to the body or frame. I usually drill a 1/4" hole in the frame someplace accessible, grind the frame clean around the hole. Then I install a 1" long 1/4" bolt, with flat washers and a lock nut and tighten it against the frame. Then I add a 1/4" eyelet to a ground wire, install it on the already tightened bolt, and add another 1/4" nut to lock on the eyelet. You can usually install several ground wires on one bolt. In a few years, when the ground deteriorates, you simple remove the bolt, clean up the frame, and install another bolt setup. I tend to add a ground to all electrical components. it solves a lot of wiring issues. Gene