The brake signal from the controller is simply switched to ground to activate the regen:
This picture shows the connections in the socket fitted on the end of the two brake lever cables:
I did try using a potentiometer to see if it would vary the braking force but it just switched from zero to 100% at one point in the angular movement.
The throttle signal is usually ~1V at rest (if it drops below 0.8V it triggers a throttle fault) and around 4.25V at full throttle.
The controller uses a working range of between 1.25V and 3.25V to go from minimum to maximum power/rpm.
The wires on the throttle will perform the same function as the ones on the MPIII but the pin allocation is different:
Alan