if the truck has no seat switch installed then it must have a circuit from the directional switch of the directional control providing the voltage input to the TB3 terminal on the control card.
It is possible the seat was changed out with a generic one? Maybe the seat switch was bypassed somewhere else in the harness?
The service documentation shows it clearly having one.
All in all if you are getting contactor operation when a direction is selected is that contactor the line contactor or a directional one?
If it is a directional contactor pulling in but you still have no movement i would check the contact tips, if they are burned chances are they are not making full closure.
But according to the troubleshooting chart the -01 code is 'no seat switch or deadman switch'.