1978 Johnson 4HP outboards Service Manual, Page 46Get this manual
eResistance of the primary winding should be 0.1 0.05 ohmsfCalibrate the ohmmeter to high ohm scale, then connect the meter red lead (+) to the "B" terminal jumper wireConnect the meter black lead (-) to the terminal inside the high tension lead coverSee Figure 4-28 general information is given hereSee Coil Specifications, Section 2IGNITION COIL TESTING (IGNITION COIL MUST BE REMOVED FROM POWER HEAD FOR POWER AND LEAKAGE TESTING
SAFETY WARNING
To avoid possible shock hazards and to prevent leakage, perform all tests to the coil on wooden or insulated bench top
If the ignition coil is good, the tester's meter will fall within the good area, with the primary circuit adjusted as specified Connect the test leads from the ignition tester to the coilConnect the black lead of the tester to the orange lead of the ignition coil and the tester's red lead to the coils orangeblack stripe ground leadConnect the high tension lead of the tester to the high tension lead (secondary) of the ignition coilWith the tester set to coil index (or operating amperageMerc-O-Tronic illustrated, adjusted as specified, note meter readingSee Figure 4-29A low reading on the tester indicates weak coil which must be replacedA dead coil will show no reading