Hartge engine conversion installation ,,help”

[Kapac]

I bought an Hartge powerbox , installed on e70 3.0D . All the connectors are in place now except 2 wires , a white one that should go to the gas pedal signal which i guess is pin 52 on dde and a grey one that sais is ,,switch wire “
Where should i connect that grey wire , is that suppose to be a switch to turn on and off the powerbox ? How should i connent it to a switch if that is where it should go .? Or should i just leave it , or get it to the car body ? Any advise is welcome. Thanks