The airbag systems in our cars or any MB cars for that matter are very finicky. You unplugging the passenger disable switch broke the electrical loop with the airbag system and it is now registering a fault with the airbag system. This part is very important. YOU DON'T HAVE WORKING AIRBAGS RIGHT NOW!!! You could slam your car into a tree at 100mph and if that light is on, they will NOT deploy. Go to the dealer and make up some excuse like you had your nephew in the car in a car seat and turned it off or something like that and when you turned it back on, the light showed up. They will know the fault had something to do with the switch being disconnected because each component has a unique ID for when the system does a self check when you turn the car on. They should be able to reset it in a matter of minutes. Words of wisdom, always disconnect your negative battery terminal for 20 minutes before you start doing just about anything with this car. It does funky stuff when things get unplugged and then plugged back in. Hope this helps.

On a lighter note, post pics of the new add-ons. I don't want to have to wait until Carlisle to see your new goodies! LOL