I have to wierd problems with my guages. When I turn my dimmer switch all the way to on to turn on interior lights my whole cluster lights up. Also when I turn on my headlights my fuel guage goes to empty, and it went up when I got gas so I believe its hooked up to the right one. I replaced the 3rd gen light switch with 4th already and just on both black connecters on 4th gen wired it to the on black one for the 3rd gen dimmer. Everything else seems to be working fine.

 

Check your ground wires.

 

On the 4th gen light switch there is a black wire for the lights and on the dimmer, on 3rd gen there is only a black wire on the dimmer switch and I wired both 4th gen black wires to the one 3rd gen one. Also on the cluster I left 2 black wires from the 3rd gen wiring unhooked that mess it up cause those the only grounds I think might be messed up. Also have a Orange and a Red wire that arn't hooked up that everything I have found they dont know where they go.