ecco cosa mi scrive un tizio americano che ha fatto la modifica:
Dear Domenico,

Good to hear from you. And yes, you can buy the TTS steering wheel and fit that into your car. But then you have to make som modifications to the wires, harness and plug. This is my recipe for doing it:

The 12 pin plug connector (yellow) on the TT MKII harness needs to have three of its wires re-assigned. Open the cover on the back of the harness plug. Looking at the plug connector from behind as if you were going to plug it in, there are 2 rows of slots, which we will number
1-2-3-4-5-6
7-8-9-10-11-12

3 through 6 are for the airbag - DO NOT TOUCH!

7 = Brown
8 = Yellow (horn)
9 = Purple
10 = Red

1, 2, 11, 12 are empty.

Push out the purple lock in the harness and then release the appropriate wire to be re-assigned.

You need to move the following wires:
move the Brown wire from 7 >to> 1
move the Yellow wire from 8 >to> 2
move the Red wire from 10 >to> 8