2003 ST 4 Stroke 9.9/15HP Johnson outboards Service Manual, Page 63Get this manual
IGNITION AND ELECTRICAL TESTING IGNITION SYSTEM ENGINE STOP SWITCH Check: ContinuityInfinity
Digital tester Tester selector:
Tester probe connection Probe Other probe Green Black Lock plate InstalledInfinity RemovedContinuity If out of specificationReplace