How to re-find and test steering wiring
If your vehicle is not plug and play then the solution is still quite easy.
With the original unit connected simply disconnect the smallest plugs one by one till the steering control does not work. it may be that the steering is in the main harness but in general this is quite rare.
1) with a multimeter you need to test each wire to see which one changes as you hold the button. This wire is connected to the AD1 wire.
2) you may also need to earth the steering so again test for this.
3) when the unit is connected you go to the steering set up page. On this page you will see the values of 255. These should now change once you hold down a button. If it does not then something is not connected correctly.