airbag light is almost always caused from snapping the slip ring wiring.
When a steering wheel is taken OFF a car (slip ring left on steering column) the wheels should be straight. This ensures the slip ring wiring is centered and therefore when the new wheel is installed, it will be correct positioning.
I believe the slip ring will rotate 3.25 times each way from centre position.
Problem comes from when a slip ring is mostly wound one way (steering wheel was turned to one side when removed and then re-installed) it can easily over extend when new wheel is rotating and snap the wires and sets off the airbag warning light.
a new slip needs to be installed.

so moral of story, is to always set wheels to straight ahead when doing a steering wheel removal.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S