When I turn on headlights I get no dash or rear.

Very often the switch contacts in high-current switches become overheated or arced, and that heat migrates out to the connector terminals. Those also become overheated which causes bad connections. Look at the old switch to see if any of the terminals are discolored. If they are, look at the mating terminals in the connector. Often the plastic connector body is melted too. The melted part can be cut away, and the overheated terminals can be replaced individually. That overheating of the terminals can carry up the wires about 4". You'll feel that part of the wire is hard to bend. Cut off all the hardened wire and terminal, splice in a new section of the same diameter wire, seal the splice with heat-shrink tubing, install a universal crimp-on terminal AND solder it, then plug that into the switch after the rest of the connector is plugged in. There's usually a second wire that needs the same repair.