I'll bet that the Jeepster and Kaiser-Frazier had a lot in common.
From a description:
The overdrive was of the automatic type; all one had to do to engage it once the control knob was set was lift off the gas pedal slightly. Pushing down hard on the gas pedal would disengage overdrive for quick passing maneuvers or climbing hills. Four-wheel drive was never offered; apparently it wasn't even considered by Willys.
Here is a link to a great description of the Borg-Warner overdrive and all the stuff that goes around it. There is a diagram of the relay, the solenoid, the kick down switch and even the rail lockout.
http://www.kaiserbill.com/Web-PDF/KF-Overdrive.pdf