Here is some info I have for the ignition switch for my 68 Chevy II Nova:
The backside of the ignition switch:
How I think the ignition switch works (and I would confirm with some tests with a meter) is the switch needs to be grounded so that when the key is turned to the crank position, the green wires connects to ground and then turns on the temp light in the dash serving as a self test to know the dash light works.
Another two connections on the key switch are for the key buzzer circuit and one terminal of the ignition switch goes to the horn relay/key buzzer and the other terminal goes to the secondary terminal of the driver's door pin switch. The driver's door pin switch should have two terminals on it with one acting as the switch for the dome light and the other terminal acting as the switch for the key buzzer circuit.
Basically the ignition switch has three different and separate circuits.
One circuit connects or disconnects power from the battery to either the accessory circuit on the car, or to the ignition circuit on the car, or to the starter solenoid circuit on the car.
The second portion of the switch connects the green wires to the casing of the switch which needs to be grounded to the car so that when the key is in the crank position, the temp light is getting power from the fuse block and now with the ground side of the temp light being grounded in that key position, the light should come on verifying it's operation.
The third portion of the switch has contact points that if the key is fully inserted and the key is in the off position AND the driver's door is opened, the switch is closed and the underhood buzzer portion of the horn relay sounds.