Had this 1989 gmc truck from almost new ,and just noticed it has floor lighting,but they do not work. checked all the fuses under the dash and they all look good.
This truck is in mint shape,still under 90,000 klm on it.
The bulbs are all good still , inside cab lights work ,thought they would be on the same fuse !
Does anyone have any Ideas where to look .

 

That is definitely a puzzler. Your interior lights are in a three way switching system. Activated by the headlight switch and the door switch.

The only thing I could suggest is start at the bulb closest to the headlight switch and start tracing wires.