TC29D - 2 Position Switch on left of dash?

[mrpeanut]

So my new property came with a TC29D which (after replacing the battery cables) seems to operate very nicely. However, of all the lights, only the headlights work. The Headlight and Hazard switches are obvious, but I can't figure out the other switch on the left...

What is the 2-position, rocker switch on the left of the instrument panel? The second position is Momentary, and the switch lights up when in that positoin... as most of the lights on the tractor aren't working, I can't deduce what that switch is for, and I don't have an operations manual. YouTube, Google, and searching TBN hasn't helped.

Seriously, what does that switch do?

 

[Ford850]

Cruise control, according to the parts diagrams on Messick's website.

 

[Halftrack]

After attaining the desired speed, that switch is pushed forward and activates a magnet which holds the speed. It should release if the brakes are pushed.