The modification that needs to be done to the guitar is shown below. The mono jack inside the guitar is replaced with a stereo jack. The additional connection on the jack (the ring) is wired to the center pin of the pot. The end pin of the pot is wired to the sleeve of the jack which is already wired to the guitar ground. You can install a new pot or usurp one of the tone or volume controls (refer to your guitar's wiring diagram).
 

MidiUp With a Volume Pedal

When used with a volume pedal no modifications are made to the guitar. A standard mono instrument cable is connected between the volume pedal and the MidiUp. The Output Jack on the MidiUp is left disconnected. The volume pedal is only used to send a control signal to the MidiUp and does not pass audio. The guitar simply connects directly to the processor or amp.

The MIDI foot controller can be used to select presets in the signal processors and select appropriate programs in the MidiUp.
 

Multiple MidiUps

There may be times when you want to have more than one pedal to allow control over different effect parameters within the same preset. For example, one pedal might control distortion while another controls volume. By using several MidiUp units you can do just that.

In the example shown here, two volume pedals are used in addition to using a pot installed into the guitar. Each of the three MidiUp units can be assigned to their own Midi channel (via a selector switch inside the box) and may therefore be programmed to transmit different Midi Controller numbers by the foot pedal. Since the MidiUps can also merge MIDI data all three units can just be chained together as shown.

You can even change assignments when you change presets. For example, in one preset you might have the guitar pot control the reverb while one of the pedals controls echo time, and in another preset you can reverse their roles so the guitar controls the echo time instead.