Full speed behind

[LanceMac]

Can't seem to diagnose or get the 3rd speed working on my 1984 Columbia Par Car Classic (36V electric).
The first two speeds seem to work ok both forward and reverse.
In this 5 solenoid setup, I found the "B" solenoid to be a 12v instead of 6 volt, so I replaced it with an OEM part. There was no change in operation.

There is a microswitch set up in the speed controller that pushes when the throttle is fully down. Nothing happens (no solenoid clicking, no change) when it is pressed. The switch has three terminals -- there is continuity across all of the terminals pressed or not, so I figured the switch is bad and have ordered another one.
My question is, what is supposed to happen when the microswitch is pressed? I can't tell from the schematic if it is supposed to be connected to the "B" solenoid or the "C" solenoid, as red wires go to both.

Any suggestions would be greatly appreciated.