I have about half a dozen backbox bulb holders which appear faulty. Tried cleaning the contacts, made sure the contacts are tight but still no joy. Getting voltage across the rear of the contacts but less than 1V. Tried re-seating the wires in case the insulation wasn't quite cut through enough but it's not that. Would anyone agree the holders have had it? If so, who supplied new ones and how do they come out? Thanks in advance for any help or info.