After tearing down the gear selector switch that I received, I can see why this is an $800 item. Lots of complicated mechanicals and LOTS of electronics!

There is a microcontroller performing all of the switch decoding and communications with the CAN bus. The mode is selected by one switch, and gear/shift direction selection is done by another. Both of these are magnetic switches with multiple hall effect transistors sensing the location of each. I believe they do this to provide the best wear and performance over time.

It's going to be tough to duplicate this function and tap into the circuit with no schematics for the PCB.

Top photo is of the PCB with switches/magnet sliders in place. The one on the right/vertical selects the mode (Automatic or Manual Shift) and the one in the center/horizontal is used to change gears in each mode.

Middle photo is showing the hall effect transistors that are mounted under the swicthes/magnet sliders.

The bottom photo is of the backside of the PCB, showing the microcontroller and other circuits.

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2008 4.8i X5 (2/25/08) 105k:
Titanium Silver/Black; All -HUD; Aero Kit; 22" VS-130 w/Pirellis;
///M Shifter & Fr Brakes; Gauge Rings; Console Pads; Custom Wheel & Mats; Roof Rails
Carbon Fiber: Int Trim, Nav Surround, Grill, Cluster Trim, Shifter & Eyelids
1.2" H&R; LUX AEs; LCI Tails; Rear Fogs; NBT EVO; ESS Tune; Meisterchaft GTC Exhaust