Gauge lights don't work

Just bought a 1990 Supra. Had a problem w/tail lights not working and the guy had wired a switch through a blown fuse to turn them on and off. Found relay was bad and replaced. Still have no gauge lights though. When you turn on the tail lights the A/C control flashes and the lights go out. Took the dimmer switch completely out but still have same problem. Any suggestions. Thanks