So the light works when I unlock the doors and when I shut the car off and open the door. If I put into the on position I get no light. The middle and rear light operate as they should. There are only two wires going to the front interior light and harness only plugs in one way so curious what I might be missing

 

Sounds like the switch itself is bad. If you know someone with a disco swap them out and see if the problem is cured. Or you could probably get new front light unit out of a junkyard for about 10 bucks. Worth a shot. I don't see how it could it could be anything other than the unit itself.

 

The front and cargo lights are identical, try switching them to test!

 

you just reminded me that I have the exact same issue. I used a test light to check it out and .....yep it is a bad switch.
I just keep forgetting to get a replacement.

 

haha I have the same issue...any time I need the light on I open the door.

 

Thanks guys. Didnt even think about checking the rear to be the same as the front. My middle light wasnt working at all and finally got to fixing it last night thinking they might be related. Not sure what previous owner had going on but they had just cut all 3 wires and they were just up there not connected to anything. Got them electrical taped back together for now but will eventually clean that up. I have some 3 wire DIY harness that I hopefully have enough wire to work with to use, or might just solder and shrink wrap and call it a day. Only bad thing about that would be I wont be able to easily take it back apart

 

Well, not sure this is the case, but I was bench testing some lights and noticed that they worked in the on position and the open door position in the car, but on the bench only in the open door position.

There is a ground(I assume) that connects to back of the light assembly. The light is held on by 2-8mm nuts that screw onto a metal chasis. That chassis has a connector(black wire) that comes out of the wiring harness. It might be the issue. When you remove the light you can shimmy that chasis out and see the connector, or lack of it.

(note: the photo is with the chassis already separated from the light and re-connected after removing from behind)

Could this be it?

 

Thanks Abran, I think that might be it. I switched out switches and switch works ok in the back. I took out that metal plate in the front and there is no wire connected to it so time to start fishing.