I understand your situation a bit clear now.
Have you had anyone put a Curtis hand set on this unit to trouble shoot the "black box" or compare the parameter setting? I would suggest you call in the Clark dealer to do this.

Johnr, thanks for the reply, my only question is that we have several of this model walkie & they all auto change direction to fwd when the belly button is pushed & stay in the fwd movement until the button is released. The unit in question only "bumps" fwd for a second & then the PLC faults out & you must disconnect/re-energize to clear the fault. All our units have the same model DC controller, so the logic, I imagine, should be the same. For safety reasons, we cannot use this walkie until the problem is fixed, due to the issue of having someone pinned behind the walkie as it will barely move fwd when the belly button is pushed. Any thoughts??

This unit has a return to neutral feature, meaning when the emergency reverse switch (aka belly button switch) is activated) the operator (or tech) needs to moved the handle to the vertical or neutral position then select a drive direction. Part of the safety feature is to disconnect any drive signal when the belly button switch has been activated for operator safety. Hope this helps.