Are you sure the bulbs are good? Test them out of the fixture. Often inheritance is a broken filament that makes and brakes itself.
Never had one of the fixtures apart but I would check for voltage directly in the bulb socket. If you have power there see how the fixture is grounded
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles