Yamaha EF4500iSE Theory & Diagnostics Manual page 39

The other type is a dual lead coil which is used in
generator applications. It has an insulated wire
wrapped around an iron core with neither end
attached to the core. Because the wire is insulated
there is no physical contact between the wire and
the core. A normal resistance test is performed by
attaching the meter leads to each end of the coil
leads.
In this case a short to ground test does apply. The
short to ground test is performed by connecting one
lead of the meter to either coil lead and the other
meter lead to the core. With the meter on the highest
ohm scale possible, it should read an open circuit.
Any resistance reading at all, indicates a bad coil.
In the generator's stator assembly, there are actually
two individual coils wrapped separately around the
same core. This is where the shorted together test
comes in.
When one meter lead is attached to any wire from
one of the coils and the other meter lead is attached
to any wire from the other coil, an open circuit should
exist.
Any resistance reading indicates the two coils are
shorted together.
Test the main and sub-coils for a short to ground.
With the meter on the highest resistance setting and
one meter lead on either the Red or the Brown wire
from the main coil and the other lead on the core,
there should be an open circuit.
DUAL LEAD COIL RESISTANCE TEST
DUAL LEAD COIL SHORT TO GROUND TEST
DOUBLE COIL SHORTED TOGETHER TEST
MAIN COIL SHORT TO GROUND TEST
2-5
Generator Diagnostics