How do I connect the mo.button to the mo.unit?

Ground signals are required on all inputs of the mo.button, as well as a constant ground connection on the black cable. The green cable leads to the mo.unit KILL input.
See wiring diagram:  wiring with mo.button

Connection to the mo.button:

         yellow — left turn signal

         white — turn signal right

         orange — light

         blue — Start

         red — horn

         purple — Front brake

         green — Input KILL (mo.unit basic & blue) / Input CONFIG (mo.unit V.2)

Connect the rear brake switch to the BRAKE input of the mo.unit.