1974 Johnson 40 HP Outboard Motors Service manual, Page 36Get this manual
bPower estIf the ignition coil is good, the ester'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 red lead of the tes ter to the blue lead of the ignition coil and the tester's black lead to the, coils black ground leadConnect the high tension lead of the tester to the high tension (secondary) of the ignition coilWith the tester set to coil index (or operating amperageMerc-O-Tronic) adjusted as specified, note meter readingSee Figure 4-23 low eading on the tester indicates weak coil which must be replacedA dead coil will how no reading BL UE BLACK