Take all safety precautions. If you get a shock, call an electrician.

Did it ever work?

If so, what changed? Where? In what way?

It's not a bulb. It's most likely called a fixture, or some other name indicating that several things are wired together.

Contact the fixture's manufacturer, if possible, for instructions. Instructions will show you what voltages and connections you should find.

Do you have two more of these things in the house? If you do, you can use a voltmeter to compare how/if those connections compare to your problem.