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When all those don't work at the same time, the usual cause is a bad ground to the fixture..........on one side or both. Some are tied together. Get a piece of wire with alligator clips at both ends and make up a test ground lead that you can attach to the metal portion of the fixture with the lens removed and the other end hooked to a good ground on the chassis and see if you have them. IF NOT, please get back to me and we can run some tests with a 12 VDC test light...........about $5 or so at most automotive stores. Great to have for this sort of thing. All follow ups are included in our fee.
Were you able to do any testing on this issue yet?