[Jack Shaft]

Coils are like any other electrical component,they need a clean dependable steady source of current.When one fails its important to check primary voltage under load..install your new coil,start engine and check voltage (at the negative side on 6v positive ground,or positive side on 12v neg ground)... if you see a big voltage drop with the engine running this could be from a poor connection or ignition switch,this will raise coil heat causing premature failure.