1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 174Get this manual
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Ignition Coil Test (Ohmmeter) Resistance tests may be performed while the ignition coil is still mounted to the powerhead1Remove the high tension lead from the ignition coil
2Separate the two-wire connector between the power pack and ignition coils3Insert jumper wire into the "A" terminal on the ignition coil end of the two-wire connector4Calibrate an ohmmeter to low ohm scale, then connect the black meter lead (-) to clean engine ground, and the red meter lead (+) to the "A" terminal jumper wire5Resistance of the primary winding should be 0.1 0.05 ohms6Calibrate the ohmmeter to high ohm scale, then connect the meter red lead (+) to the "A" terminal jumper wireConnect the meter black lead (-) to the high tension terminal of the coil7Resistance of the secondary winding should be 275 25 ohmsReplace the ignition coil if the reading is other than specified8To test bottom ignition coil, repeat the above procedure using terminal "8" in the two-wire connector9Test resistance of high tension leads on low ohms scaleResistance should be near zero