these are built similar to the ray/cat reach trucks
only place there are circuit boards are under the top cover maybe and the panel behind the operators legs where the contactor panel is (the tmm and fuse/relay board are mounted in there).
If this unit was in a bad storm as he indicated in an earlier post, there is a high likely hood that water got in somewhere.

EDIT: ok this is an earlier design, the TMM, power distribution board etc are all open so if water came in it most likely got something wet. But i'll look at the photos and see if i can mark them up and show him what's what.
i got the pictures from him.
If memory serves me right on this truck the deadman circuit goes straight in to the TMM so if the switches aren't bad then, you guessed it, something is wrong with the TMM or the wiring.
But then again he's not a mechanic so we don't know if he put the deadman switch in right, (he said he replaced it). It may be wired in backwards for all we know.
He really needs a lift tech to look at it imo.