I was having the same issue, but the bulb would intermittently work. I changed the bulb with another bulb, and all works fine now.
Perhaps there is a break in one of your wires. Have you had anyone install an aftermarket stereo system? Perhaps they pinched a line when putting the car back together, or put a screw through it.
It might also be that the socket is missing a wire connection that used to be there and possibly broke off?
I would take out the bulb holder, and get a test light and test the wire. if the wires are all working, then the problem is most likely in the bulb unit or the wiring in the bulb unit.
Sometimes the metal pin in the bottom of the bulb socket can get pushed in and might need to be adjusted.
Test the wires, if you get a failure there, then I would think about tracing the wire to see if it is pinched or cut somewhere.
If the insulation is exposed, it could also be grouding out on the chassis.
I'm no expert here, but I do know a thing or two about things that can happen at stereo shops. I've seen people put screws into gas tanks, and clip wires before. Its not too uncommon for it to happen. sometimes when putting the car back together, they can accidentally cut wires.
In anycase, good luck. I'm sure if the wires check out ok, then it has to do with the bulb unit or the bulb socket. If the bulb is working fine then I can't see anything else that could cause it, unless there is some switch or computer that is involved with it that is failing.
Whatever you do, Don't take my word for it, I'm not an expert in any way, but if you do a little testing, you might be able to isolate the problem to a wire, connection, or other fault.
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