Service manual

STP 11-25R13-SM-TG
L - 1
APPENDIX L – COIL GUIDELINES
L-1. Malfunctions.
A coil can malfunction in either of two ways: an open or a short. The most common instrument used
to check a coil is an ohmmeter.
L-2. Resistance.
A good coil should have some resistance from one end of its wire to the other, but it should not read
infinity. If it does, then the wire is broken. This is an indication of an open coil.
L-3. Shorts.
A short may be more difficult to find. If two of the windings short to each other, then the total
resistance of the coil may not decrease enough to give a different reading on an ohmmeter. In such
cases, eliminating the other components in the circuit may be the best method for determining whether
the coil is good or bad. Comparison with a known good coil may be the only way to tell for sure.
L-4. Winding Shorted to the Core.
If the coil's winding is shorted to the core, then an ohmmeter can be used to find it. With most coils,
the core is insulated from the wire and an ohmmeter should indicate infinite resistance between the two.
A low resistance reading would indicate a short.