Just bought a 70 Monte. When I pull out on the headlamp switch all exterior lights come on as they should. The radio and heater control lamps light up too. The problem is the three main instruments, fuel gauge, speedo, and clock, will not light up at all. In fact when the headlamps are on the turn signal indicators on the dash stay lit. The turn signal and four-ways work when activated as do the indicators. When operated the dimmer control on the headlamp switch dims and brightens the radio, heater control, and turn signal indicators so the problem doesn't appear to be the switch. I also replaced the SFE4 fuse for the dash lamps with no luck. Has anyone experience such a problem? What could the problem be? Any help is greatly appreciated.

 

You may have to pull the cluster out and see if it is any of the bulbs are toast, with the signal light staying on, have you checked all your signals and tails to make sure non are burnt out? Usual it staying on is an indication of that,

The only other thing I can think of is maybe the ground for the cluster lighting has come loose or corroded or damaged in some way

 

id check the bulbs in the 3 gauges you said dont light up, and then check the wiring.