To be certain, you should:
* Consult your owner's manual: This is the best source for the specific location in your vehicle.
* Look up a diagram online: Search for "1999 Chevy S-10 [engine size] ignition coil location" using your specific engine size (e.g., 4.3L V6 or 2.2L I4). Many repair manuals and websites offer diagrams.
It's usually a black cylindrical component, sometimes with several wires connected to it. Be careful when looking for it, as the engine compartment is hot when the engine is running.