On a 1971 Pontiac Firebird's ignition system, the wire you need to remove to run an HEI distributor is the
ballast resistor wire. This wire is in the circuit to reduce voltage to the points in the original ignition system. The HEI distributor doesn't need this reduced voltage, and the ballast resistor can actually damage the HEI module if left in the circuit.
It's usually a single wire connected to one side of the ignition coil. You'll need to trace the wires to be absolutely sure, but it's often a light-gauge wire and easily identifiable by its connection to the coil. A wiring diagram specific to your year and model Firebird would help you positively identify it.
