Matt -
You can't mix lamp leads and A/A1 on the same terminal. They used to make little holders for the spade leads (when you ran out of terminals), but you could always give them a little twist of wire and then some tape.
The ground off hook was designed for dial access to PA systems (as I recall). You went off hook on the ICM, dialed a number that pulled in a relay that would connect ICM T&R to a WMT1 matching xfrmr that would connect to the input of an amplifier. (we used to switch ground through the ICM and leave one side of the buzzers leaning on battery). The off hook ground held the relay up while you paged. When you hung up, the ground went away, the relay dropped off and was available for the next page.
Sam
