This retrofit has been succesfully implemented and tested on mine A4 B9, and it’s still active.

Telephone bracket (wireless charger) R126 – T6ez –

• 1 – Terminal 30 12V [SC2]
• 2 – Switch-on signal from control unit 1 for information electronics – J794-
• 3 – Status signal to control unit 1 for information electronics -J794-
• 4 – Terminal 31 GND [Earth point 687] 
• 5 – Wake-up wire to entry and start authorisation control unit -J518- / onboard supply control unit – J519-
• 6 – Not used

MIB2 (12-pin grey connector) J794  – T12n-

• 1 – CAN bus High to keyboard unit – E380 / display J685
• 2 – Reset to multimedia system operating unit – E380-
• 3 – Open circuit diagnostic lead
• 4 – Not used
• 5 – Switch-on signal to telephone bracket – R126-
• 6 – CAN bus High (infotainment)
• 7 – CAN bus Low to keyboard unit – E380 / display J685
• 8 – Reset -J794- from keyboard unit – E380-
• 9 – Not used
• 10 – Not used
• 11 – Status signal from telephone bracket – R126-
• 12 – CAN bus Low (infotainment)

CODING:

5F INFORMATION ELECTRONICS – CODING

• Byte 15 
  • Enable bit 0 Baseplate
  • Enable bit 1 Antenna_baseplate (only if signal booster is installed too)
  • Enable bit 5 Wireless_charging_avaiability