to replace the cables running to the traction motors, my guess at the OEM was most likely a #1 gauge wire, I might use 1/0 or 2/0 welding copper cable, that I got at the local welding supply house, but take a sample. they can get you the eye-lugs (ends) that will match, too. use the same size as all the rest of the cables to that same motor.

also, it's worth noting here, that when you see a rec gate on with a test load like a light bulb, you are trying to check something's ability to carry 500AmpsX36Volts=180000watts using something like.03 watts. that does seem to fail more 'under load'.

fix the power cables