To be certain, you should:
* Consult your owner's manual: This is the best resource for the exact location.
* Look at a diagram: A repair manual or online diagrams for your specific engine (AMC 360 V8) will show the PCV valve clearly.
* Search online: Images of the AMC 360 V8 engine bay for a 1990 Grand Wagoneer can help you visually locate it.
Remember that working on your engine can be dangerous. If you're unsure about anything, consult a qualified mechanic.