A bit of cutting and a bit of filling with metal based filler gets us a shape similar to a E36 base on our donor E46 steering wheel.
Unfortunately I don't have pictures of the steps to get to this point, but basically I made a plaster mould of the E36 base, trimmed the E46 where necessary, put the metal filler in the mould and then pressed the E46 steering wheel base into it. Then broke the plaster mould and was left with what you see.
At this point the project was put on hold for quite a while as I was having difficulty getting the extra connections from the E46 through the E36 slip ring.
It was then brought to my attention by KennyKen that the E39 actually had a similar slipring to the E36 but also had the MF connections.
An E39 slip ring was duly obtained and sure enough, the fitting is the same and it does have the extra connectors required.
Here's the E39 slip ring, complete with the 3 extra wires going through it that do the iBus and cruise control. The Ground for the iBus is common with the horn, so the third wire takes +12v to the switches.
Now the connectors at the steering coloumn end are the same as the E36, so should just plug in. I have obtained some extra pins to go in the longer connector for the iBus and 12v, these will be extended to the back of the car where the PC is.
however the connectors inside the steering wheel don't altogether match up, the iBus, 12v, GND are cruise do actually match up as they have the same end connector which plugs into the switch boards. However the airbag and horn on the E46 have a 4 way plug, whereas on the E36 the airbag was a two way and the horn had a spade and loop connector.
A quick bit of soldering and some heat shrink and we now have a male connector for the Airbag and horn.
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Here is the Slip ring connected to the back of the steering wheel.
And this is how it will look with the airbag in place
Now to fit it into the car.