A 4-cylinder engine only has 4 spark plugs, one per cylinder. A 1996 Ford Ranger 4-cylinder engine definitely does *not* have 8 spark plugs. There's likely a mistake in your observation. You may be miscounting, or there's something else going on with the engine (e.g., it might not be entirely stock, it might have extra wires for some reason).
To find the location of the spark plugs, you'll need to consult a repair manual specific to your 1996 Ford Ranger 4-cylinder engine. These manuals will show you diagrams of the engine bay and precisely where each spark plug is located. You can find these manuals online or at auto parts stores.
