This website has lots of good info on wiring & accessories etc, one of the pics shows the general location where the courtesy lights mount on the dash, they are just mounted with a small screw into the lower metal frame of the dash in each corner. I can get a pic of my car later today if needed.
Also, strongly suggest buying a GM/Pontiac service manual for your year, it will show things like this as well as most all other aspects of working on these cars the correct way, much better than searching youtube or google, should be able to find them on CD for cheap.
https://firebirdtransamparts.com/