Bob k,
if your getting any type of electrical current through the throttle cable it sounds to me like you have something in the electrical harness shorting out against that cable somewhere. Make sure the cable isnt rubbing against any electrical switch or terminal anywhere under the floorplate or panels. I'm sure the ground straps will help somewhat but it also wouldnt hurt to double check your harness and cable routing. NO electrical current should go through that cable whatsoever. It's gotta be comming from somewhere.

And as has already been mentioned:
Unfortunatly most if not all lifttrucks of this type mount the hydraulic pump in the rear subframe inside the counterweight and is driven from the front of the crankshaft of the engine via a yoke and driveshaft. There are a few models that do drive the pump off the transmission like the S model hysters or some of the older trucks that mount the pump on the timing cover housings, but you dont see those much anymore.

Anyway that shaft/yoke will have to be taken loose to change the belt. There should be 4 13mm or 1/2in bolts to remove before the yoke can be slid back away from the harmonic balancer/pulley. Once those are removed the shaft will slide enough to get the belt off.

As for moving the pump? No you dont have to.