Reversing light switch.

Good evening. My first post and I have a problem .

I need to locate the switch which controls the reversing lights as I believe it's faulty. A number of things which should happen when reverse is engaged don't happen. The reverse lights don't come on, the reverse warning beeper doesn't work, the rear wiper doesn't come on when the front wipers are working and the radio sound is not lowered.

I am assuming, possibly incorrectly, that all these things are controlled by the same switch so I'm guessing that I need to replace it. However, in spite of half a day spent Googling I can't find a definitive answer. It seems that the switch is screwed into the gearbox on the right hand side  I have removed the undertray but I can't locate it. It appears that the actual switch is an inexpensive item but I shudder to think what our local Audi dealer will charge.

The car is a 2010 A4 B8. Six speed manual, diesel 2.0 tdi 143 cv.

Any help would be much apprecated.