Cant speak to the truck, might be for a light that was never installed. On aircraft all of the control surfaces are grounded to the frame. static electricity will build up on the surface and then discharge through the bearings for that surface creating a mini arc welding effect.

Cant see this happening on truck though, so ground for non installed underhood light(edit: meaning I am guessing for hood light grounding purposes). I cannot believe that the hood is not grounded enough through the springs to discharge any static built up from the nominal air velocity across the hood.