in addition to edwardt's advise this might help some

here is a trick you can do that will help with the motor circuit checking, its quick and will let you know right away if a motor circuit is working ok when turning

- get some blocks small enough but stable and strong enough to put under the front mast legs and tilt forward onto them to lift the drive wheels up off the floor.
- then get on the truck and drive it in both directions while turning the steering and take note of what each drive motor is doing while doing this test.

In straight forward and reverse direction both wheels should be turning in the same manner at the same speed during acceleration and normal driving.
when you turn left the left wheel should start slowing down at certain points and come to a complete stop when at almost full left turn and it may even reverse direction at full left turn.

do the same thing turning the steering in the right side direction and the right motor should do the same thing.

if there is any problems with either motor you will see it and then be able to determine which circuit to test for either a bad motor, bad cables or a bad contactor.

Keep in mind since this is a dual motor setup there will be 2 sets of forward and 2 sets of reverse contactors so check them carefully during the operation also, they should be located just behind your feet behind that panel.