2005 Yamaha F90TR 90HP Outboards Factory Service Manual, Page 213Get this manual
Starter motorCharging system Armature continuity Commutator segments Segment Armature core Segment Armature shaft Continuity No continuity No continuity 3Connect the negative battery lead to the starter motor bodyBr
Checking the brushes
1Measure the brush lengthReplace the brush assembly if below specificationS6D88130
CAUTION:
Do not connect the battery for more than one second, otherwise the magnet switch can be damaged4Check that there is continuity between the magnet switch terminalsReplace if there is no continuity5Check that there is no continuity after the negative battery terminal is removedReplace if there is continuityNOTE: The starter motor pinion should be pushed out while the magnet switch is on