Had a quick look at the TT wheel earlier, then dug out an old mk2 one from the shed. So basically I need a horn contact ring on the back of the TT one, and wire it to the horn push, deleting the airbag. Hmm, that was easy to separate. Not tried it on the Audi one yet, and will need to drill for wire to go through probably. Next installment soon.
Spent a bit of time measuring stuff, and figuring out things. The contact ring from the mk2 has the wire on a 'post' which I presumed would need a hole drilling, but this lines up with one hole in the tt wheel. TT wheel fits straight on the large spline column, but there is a gap between wheel and column shroud, and so a packer/spacer is required to fill this and mount the horn contact ring so it works on the column pick up point. 90mm external, 42mm internal and 15mm thick should be a good starting point, bit of lathe work coming up me thinks. Next, wiring. Mk2 uses earth via the column itself and then the switched wire goes to the contact ring. TT has a plug that goes in the clock spring unit as it has the airbag, so remove the wiring for the safety system, then left with 2 wires for the horn, brown and black. The new wheel runs separate earth to the horn switch, totally independent of the alloy body, so I will connect the earth wire to the wheel's skeleton so it picks up from there, and the black wire from mk2 contact ring is long enough to replace the TT one, completing the horn circuitry. It seems a little too simple so far, sure there will be problems in the pipeline soon.
Made a spacer this morning, quick bit of router work and squirt of paint, will see how it fits later in the car.
Got home, stripped the firing mechanism out of the airbag, 6 nuts and the nasty bugger is gone. Put the wheel in place and tested the spacer, everything works perfectly, horn, indicator cancels normally. Airbag centre reattached to the wheel, and that's it, extremely simple. Will probably make another spacer, or get one 3d printed even, beaten it up a little more. So, overall I'm quite shocked at how simple it was, read threads of people fitting other wheels but horn and indicator bit not working. This all works on mine. May open up more possibilities with later flat bottom steering wheel, prices coming down now on them, but this has cost me a tenner, and is a nod to the drive trains roots from Audi. Hope this helps. Cheers Dave
Cheers @rubjonny , glad I've finally done something useful, I'll get a proper drawing done and posted for the size spacer I used.