Also check the grounding at the light itself. How they are grounded depends on the year, at least on T2's and T3's, likely the same on bugs. If the lights depends on the screw that attaches the housing, that may not be sufficient enough of a ground. I've run separate ground leads from the light housing to solid ground to avoid this problem. Check power at the light using a separate ground point. If power is there, then it's the lack of grounding. Later models had a separate ground and didn't depend on the housing attach screws.
