the switch is a "window" switch.
It makes contact at a certain angle of the paddle. Outside that "window", it is open. The WSM outlines it pretty well.
On a 3901 you can do a quick easy diag using the beeper.
start with key OFF
hold down both of the yellow buttons
now turn the key on while holding the buttons down.
Look where the hour meter is. Should say "a". If it does, let go of the buttons. Now hold them down again until you get a beep. Soon as you hear the beep let go of the buttons. Meter should say 1: and then some numbers. Those numbers don't matter for what you are doing.
now you can actuate your switches. Each one you activate should make a beep. HST pedal forward, should beep. Return to neutral, should beep. Park brake lever, should beep. PTO switch, should beep. Now flip the seat up and actuate the seat switch. It should beep somewhere in the middle. If not the wiring or switch is suspect. I've seen the wires get ripped out of the connector before. U can test all of the switches that way. It is super super easy!