E1200? or E12000?
on the E12000 the codes:
-64 means the line driver input (P2-17) is less that 12% of battery volts.
-65 means the line coil is too high during the run mode.

i would check the line contactor.
check the coil resistance, should measure 59ohm for 36/48v trucks, 161ohm for 80v trucks. also check the signal on that wire 17 on P2 connector and make sure there is a signal when the truck is turned on.
if all that checks out ok then you have a bad controller unit.

Swoop modelE1200 has a 64 and 65 code can you point that direction
Tanks

DTC 65
Pump Inverter Fault

see your mail for information on how to troubleshoot this