Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 82Get this manual
4Check rotor for short to groundNO CONTINUITY should exist between slip rings and rotor shaftIf CONTINUITY exists, rotor is defective STATOR TEST
1With rectifier removed, use an ohmmeter to check for short circuit between each stator lead and the stator frameIf CONTINUITY exists, stator is defective