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The first thing hat needs to be done is use a scan tool to see what fault codes have stored in the ABS module. When the airbag light is on it's because the airbag module has seen a problem somewhere in the system, turned on the warning light and disabled the airbags.
The problem could be a number of things. It could be anything from either of the airbags to the airbag module itself, the clockspring in the steering column, or wiring between any of the components. One of the most common causes of an airbag light is the clockspring, which is in the steering column behind the wheel and is what makes electrical contact between the wheel and column.