Brake ground

take out housing and put it back in with a spikey washer under a nut
take out holders clean polish, give the contacts and bulb collar a clean, check that the cardboard/fibreboard disk and solder buttons are good and the spring underneath is not shorting to the wire or the back of the contacts put em back in

if you have any wire bolted to a screw in the trunk floor undo it clean it spikey washer it and put it back with a smear of grease over it

might work... :)

Dave