How to start my '74 without a dash?

Whatever you do tape the ammeter wires off for safety. If you leave them unhooked, you won't have to worry about anything in the dash shorting, an unhooked connector

Easiest way to hot--wire a 70/ later car is to hook a clip lead from the battery to the BLUE field connector on the alternator. This puts the ballast resistor "in the circuit" and you can jumper the solenoid.