Does anybody know where these plug into?

As you probably know, Engine and Instrument Panel wiring harnesses changed every year. Sometimes even mid year changes took place.
In 1975 there was only one Instrument Panel wiring harness: part number 3843142. All the interlock connectors were in the harness, just like in 1974 including the green control unit.
Part number for the Instrument Panel harness changed in 1975 because other modifications were made that had nothing to do with the interlock system.
As mentioned earlier, the green control unit was kept in place but was disabled on October 31, 1974.