So the only guages without lights are the factory guages? Your ISSPRO guages and tail lights, in the same circuit work fine?
If your ISSPRO guage lights and tail lights are working, it's not a fuse or the headlight switch. I would start checking all of your connections, especially the splice point where you tied the ISSPRO guages in with the factory circuit. I've had a bad splice come apart and do this.
Then check your ground, should be on the right side of the steering column. The Isspro guages and tail lights should have a seperate ground from the factory guages.
Hope this helps.
Tom