The switch on the side is the third gear switch. It closes when third gear is achieved.Also the power side has a brake light switch circuit, when you apply the brakes, it cuts the power to the switch and the converter unlocks.
If you mash the accelerator and the trans downshifts to seconfd , the 3rd gear switch opens and unlocks the converter also, untill it upshifts.
The ground is controlled by the ECM on most of them,turning on when a required speed is achieved, along with 3rd gear, and minimal throttle inclination.
The vacuum switch is for the distributor vacuum , cuts it off, during deceleration IIRC.
Fact is stranger than Fiction