Either there is current to the lights or there is not. An Ohmmeter should reveal this. Either you have a good ground or you do not. If you have current, the ohmmeter will indicate the ground. If you do not have current, you can reroute an external wire to check the ground.

Odds are, it's one or the other, unless the bulb or the socket are bad.

Everyone hates electrical problems. It is my view that the basic problem is due to the fact that electricity is invisible.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)