To be certain, you should:
1. Consult your owner's manual: This is the best source for the specific location on your truck.
2. Look for a small switch with one or two wires connected: It's usually a relatively small, cylindrical component.
3. Refer to a repair manual or online diagrams: Searching for "[your engine size] 1997 Chevy Silverado oil pressure switch location" will likely yield diagrams showing its position.
Be careful when searching for it, as the engine is hot after running.