I'm not sure I understand this sketch:
It looks like there are two battery packs wired in series. The upper pack is charged by the LiIon charger, while the negative of the lower pack is connected to the controller (-) terminal. The top (+) of the pack goes through a fuse and the contactor (with precharge) to the controller (B+) and one terminal of the motor (Field?). There are two motor terminals connected together (Armature and Field?) to the controller (A) terminal. And the other motor terminal (Armature?) connects through another fuse to the controller (M-) terminal. So I'm assuming that the controller M- uses PWM to adjust current through the series wound motor and it shunts some current from B+ to A for field weakening?
But what really confuses me is the ON/OFF switch which connects the midpoint of the battery packs to ground. This won't do anything unless something else is connected to ground. I'll make a WAG and say that the coil of the contactor (which is not shown) connects from the lower battery pack (-) to ground, and the switch completes the circuit. If these grounds are the car chassis, rather than a separate wire, then the connection may be intermittent. AFAIK most EVs do not like to have anything grounded. But if the bottom battery pack is actually the 12VDC accessory circuit the its (-) terminal should be connected to the chassis so the lights and fans and other things will work as usual, although I think most modern cars do not rely on the chassis for current return.
I had to redraw the schematic. It looks like a bucket of worms!