Daughters 72 dart not turning over
The terminal with the G.
On a '72 w/ automatic the wire may be a brown with yellow stripe.
Break or partial break could be in the wire to the switch, or the connectors, or the neutral safety switch itself. Making a jumper going from the G terminal to a ground will eliminate those. If so, then you where to investigate.
Its supposed to work like this:
When the key is in Start position, power becomes available in the yellow wire going to the I terminal.
When power goes from the I terminal through the G terminal to ground, an internal switch connects the Battery terminal to the Solenoid terminal.
Power then flows to the starter solenoid in the starter.