Quite the assumption on the k2 relay pins... I highly doubt that is his problem. The Easi order picker does not use a k2 relay for braking, neither does it have a fuse relay card. 5400 on the other hand... yeah..

Added. Removing your foot from the deadman while traveling will cause the truck to plug to a stop as opposed to applying the brake like when the truck codes out or the epo is depressed.

Maybe they should have hit the epo switch when trying to recreate your accident instead of using the deadman, in either case it sounds to me the truck did what it was designed to do and ceased travel may it be from an abused battery or a component failure in the drive system.