good thought rafarmer but that 1234E isn't designed for pallet jacks, it is more for the bigger sitdown riders that have drive and hydraulic electric controls, hence the dual pot inputs, one for drive and the other for hyd input. Most pallet jacks don't have variable hydraulic controls, they are self contained hydraulic units with pump, motor, resivoir all contained in one unit , it's either 'on' or 'off'.

As for the drive controller in the jungheinrich units i can say with some certainty they are not made by Curtis, most of the ones I've seen look more like something danaher or sevcon but from what i understand is they design their own. I'm sure some other company manufacture's them for jungheinrich but they do have jungheinrich labels all over them. So whomever actually mfg's them is a mystery. Maybe if the cover could be removed that might reveal something internally, and to be honest I've had the cover off one of these controllers but unfortunately i wasn't looking for secret mfg labels, was looking for loose ribbon cables on the circuit boards ;o) (a problem they had early on)

As for hooking a handset to it to adjust settings? i wasn't aware that could be done, the db9 serial connector on this unit was designed for laptop connection using their AC controls software, i am not aware of any jungheinrich handset. (not saying there isn't one, I've just never seen one)

I'm still leaning towards some kind of programming adjustment or possibly even a defective tiller control.