When I purchased my new to me 2008 Silverado the dealer told me they disconnected the passenger side. How can I turn it back on. I'm tired of seeing Service Airbag. Where are the impact sensors located on the front. Thanks.

 

That sounds like it might have been illegal to do to me as it's a safety issue. They likely disconnected it as there was something wrong that they did not want to repair.
I'd call the Bureau of Automotive Repairs on their *****, if I were you.Too h**l with repairing this condition on your dime, man! Cheap b*****d's need to be held accountable.