1978 Johnson 4HP outboards Service Manual, Page 43Get this manual
IGNITION SYSTEM TESTS USING C.DVOLTMETER TESTER
aMeter reading 230 or higherGo to Sensor Coil Output TestbNo readingCheck for short to groundcLow reading, check resistance of charge coilIf resistance does not meet specifications, replace charge coilTo check for short to ground, remove black meter lead from cavity "0" and ground to armature plate groundSee Figure 4-24Crank engine and observe meterRemove lead from cavity "0" and insert into cavity "A Crank engine and observe meterAny reading on either test means charge coil is shorted to groundLocate short and repair or replace charge coil