-Correct. You need to get the engine model # that is stamped into the shroud, usually above the spark plug. It could also be on a sticker on the engine if you have one of the newer Tecumsehs before they went out of business. The spark plug wire is permanently attached to the coil, so if you need a new plug wire, then you have to buy the coil. You can find new ones on eBay for around $20 with free shipping. Just make sure you get the correct one for your engine...
Tecumseh Ignition Coils
L8R,
Matt