I was having problems with my light bar. Turned out it wasn't grounded well, especially after I had finished spraying several coats of paint on it.
My fix was to solder seperate ground wires to each of the sockets, tied all these together and then connected to chassis. It now works whether it's connected or not, and much brighter.
I plan on doing this to my rear tail lights when I get the time, the ground connections on these cars are marginal at best.
