Before modern battery coils and electronic control units, vintage tractors relied entirely on mechanical magnetos to generate spark. Geared directly to the engine camshaft, these self-contained units produced high-voltage electricity mechanically, requiring no onboard battery. A well-adjusted magneto allowed a tractor to sit unpowered for months and still fire reliably with one good c... https://www.homepros411.com/blog/how-to-revive-an-old-tractor-engine-that-has-sat-for-years