The governor--not Ed Schaefer, is a switch that closes and grounds to send power thru the relay to the solenoid. At about 28-30 mph (cut in speed) the governor closes the circuit and the pawl of the solenoid can push out and engage the planetary gears. This is like in the song--"I took my foot off the gas, and man alive, I shoved it on down into OVERDRIVE." That is what you do--you take your foot off the accelerator and the transmission automatically shifts into OVERDRIVE.
The governor is threaded and screws into, usually, the right rear (passenger) side of the overdrive tailhousing.