So, after a bit more looking, the PO had 36v going to forward and reverse. I ran it like this for several weeks without issue, other than reverse having more speed/power than forward.
I have moved the right red cable from the first battery to the fourth(counting left to right). See here for where it is attached:
Here is a closeup of the F/R switch:
Here is the battery wiring PRIOR to moving the reverse to 18v.
Here is the micro on the F/R switch:
The blue goes to the ignition, I think. The yellow goes to the speed control box.