In my Ventus 2 there is a thin a fiberglass rod attached to the flap control rod. The thin fiberglass rod runs to a switch reading box behind the seat next to the wheel well where all the sensors are enclosed. I would guess there is a Hall switch magnet attached to the rod inside the box to activate each of the sensors. Designed like this you do not have to try and attach everything near the flap handle.

The flap indicator is one of the surprises that I have found I would hate to do without now.

A low tech system I have seen is to run a plastic or fiberglass rod forward to the panel from the flap control rod and put a mark or the rod and set up a scale on the panel. Pure mechanical with no electronics.