1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 227Get this manual
ARMATURE TESTS Testing for Shorls;
Check armature on Growler (foll ow Growler manufacturer's leS ins truc tio ns)Indication of sho rl req ui res replacement of armat ure
Test for Ground: Use Ohmmeter (R scale), Place one lead of Ohmmeter on armature shaft and other lead Oil co mmutator as shownIf Olltinuit }' is indica ted, arma ture is grounded and mus be repla ced
Checking and Cleaning Com mutat or:
If commuta to is worn it can be tur ned down on an nna lure conditi oner 1001 or on lathe