HFR_Racer - did you ever solve this problem? I have an 88 with what appears to be a similar wiring setup - same fusing as yours. My radio and interior cabin light work fine - cabin light goes on when I open the door, without the ignition turned on. Neither the front trunk light nor the glovebox light are working. The filament in the trunk lamp appears to be intact. Not showing any voltage across the bulb terminals though, regardless of plunger switch position.

I'm not nearly as good with electrics as it sounds like you are - just curious how you ended up resolving this. Thanks for any input.