The secondary air injection (AIR) system on a Chevrolet S-10 is generally located near the exhaust manifold. It consists of a pump (often electric), tubing, and valves that route air into the exhaust system during startup to help catalyze the combustion of unburnt hydrocarbons. The exact placement of the pump and related components can vary slightly depending on the year and engine of your specific S-10. You'll likely find the pump somewhere in the engine bay, near the firewall, and the tubing connected to the exhaust system near the catalytic converter or upstream.
To be absolutely sure, you'll need to consult a repair manual specific to your vehicle's year and engine. A Chilton's or Haynes manual would be a good place to start. You can also find diagrams online, but using a vehicle-specific manual is always recommended for accuracy.
