have you fitted new controller and had them programed. i had code 51 last week. see the little blue current limiter that bridges across the line contacter ,that allows the capacitors in the controlers to power up before the controller will pull in the line contacter. watch out it may be hot. you could try dissconnecting battery and discharging system by pressing the horn ,leave it for 15 mins then try again. a lot of key on/offs can cause this fault code to kick up

now it is giving a code 51

I would also say to be sure you check ALL the power fuses OUT of the truck, don't trust that you can see the blown fuse from looking in the little glass window...

i had a machine do this about a month ago
both controls were fried and had similar codes in both boxes (clark 3 wheeler with individual motor controls and contactor pump)

remove all the cables and the plug
check for continuity between the A terminals and the heatsink
no continuity should exist

then do the same for the field, B+, and NEG terminals to the heatsink
again no continuity should exist

then check for continuity between all the heavy terminals (b+, A1, A2, F1, F2, and NEG)
the only two that should have continuity is B+ to A1 the rest are isolated by the internal transistors with the power off and all cables removed

if you take that cover off youll most likely smell that it burnt up before you see it lol (i know i did)

if not check the motors for shorts

this one has 2 different sized GE boxes?
it would help to have the beginning part of the serial number or the complete model number (or both lol)

check drive motor for shorts.if all ok take the lid off the controller you may find some blown out transistors usually caused by sticking brakes or shunting pallets

rectangle stripped black with a GE emblem in the top right corner

is that a three wheel style truck with 2 drive motors under the footplate. code 66 and 67 are shorts in the left drive motor field. but it maybe a blown controller. describe the controller striped square box or oblong grey