GMC 1976 ZEO 6083 Maintenance Manual page 713

24C- 36 ONAN MOTOR GENERATOR
SWITCH ASSEMBLY
Place armature in growler and hold a thin, steel
blade (hacksaw blade) parallel to the core and just
above it while slowly rotating armature in growler.
Figure 64-Testing for Grounded Armature
Figure 63-Starter (6KW)
A shorted armature will cause blade to vibrate and
be attracted to the core.
Figure 65-Testing for a Short Circuit