Where are the spark plugs on a 1999 Oldsmobile Alero?

The spark plugs on a 1999 Oldsmobile Alero are located on top of the engine, under a plastic cover. To access them, you'll need to remove the plastic engine cover. They're arranged in a V-pattern following the cylinder arrangement of the engine. You'll likely need a spark plug socket (usually 5/8" or 13/16", double check with your owner's manual) and a ratchet to remove and install them. A good quality spark plug socket will prevent damage to the plugs.