Sierra s 18-5181 Ignition Coil is designed for use with Johnson/Evinrdue and Mercury/Mariner outboard engines. It features a primary resistance of 0.09 +/- 10% ohms and a secondary resistance of 10 +/- 15% ohms. Includes one ignition coil per package. It is interchangeable with Mallory 9-23102; CDI 183-4477; GLM 72100; Mercury Marine 802371 and 802371A1; and Johnson/Evinrude Outboard 0580416 0580971 0582370 0582931 0582995 and 0584477. Each Sierra product meets or exceeds the original equipment part it replaces.