Window Switch?
This is what i feel like! - the drivers side button has gone bad or
- there is probably a short in one of the traveler wires between the two switches.
If you get a hold of a schematic, you can test the switches easily. The F-Body factory manual has all of the car's schematics in it, which is a great investment. However; the material is under copyright and can't be legally posted online.
Unfortunately, toggling the buttons at the same time will not prove anything out for you. The circuit should work fine if both buttons are pressed in the same direction but should cut out if they are pressed in opposite direction. If it doesn't behave that way, it still could be a wiring issue - so you will need to test the switch with a continuity tester to make sure.


