You didn't mention your car year, so you're getting my comments based on my 1995/1996 Electrical Trouble-shooting Manual (ETM). As an initial WAG, it sounds like its the door switch or the wiring to it.
I put a lot of steps here. I'm an electrical engineer and so this stuff is obvious to me, but understandably is not so obvious to others. Do what you can, or provide this info to someone who understands wiring. Feel free to ask questions & let me know how far you got. I can suggest further tests based on what you find.
The most direct approach (ie, not using a voltmeter) is to open up the door and find the switch. Is connector C615 connected to it? The switch side of the connector has RED and BLK leads; connector C615 (2 pins, GRY connector body color) has GRN/BLU and BLK leads.
If C615 is not connected to the switch, that was probably your problem.
If the switch is connected, remove the connector and take a piece of wire (a paper clip will do) and short the leads together (GRN/BLU to BLK). If all 3 lights come on, the switch is broken.
If lights don't come on,
1. You can have a bad ground in the door
2. You can have a broken (cut??) GRN/BLU wire in the door
or
3. C409, the main electrical connector to the door, may be disconnected. The ETM indicates that C409 is in the upper left corner of the driver's footwell, behind the kick panel. Remove the two screws to drop the panel above the driver's side foot well. That will expose the timed foot well light. Then, remove the left kick panel. I've never tried to locate it, but the ETM says C409 is colored GRY and has 14 pins (see photo 45 & page 203-14 in the ETM). You can probably find it from the door opening side by following the harness between the door and the body.
If you can use a voltmeter, the courtesy light is in the panel you dropped.
Is there +12V on the WHT/BLU wire at the light assembly? It should be there even with the ignition off. If so, there is power to the foot well light and ignition key light. That same WHT/BLU lead goes through C409 to supply power to the courtesy light in the driver's door.
A GRN/BLU wire appears on connector C409. It may be possibly to probe the back side of the connector & short that lead to ground. If you ground that lead and any of the 3 lights come on, its a wiring problem in the GRN/BLU wire between the door and C409 or a bad ground to the door, G401. G401 is wired directly from the door to a wire that is grounded to the left and below C409. (Photo 46 in the ETM)
