A digital multimeter will be needed to test the field coil assembly. While testing the field coil assembly, safety glasses and protective gloves need to be worn.
In a series, parallel, or compound wound starter motor the complete circuit or electrical path, i.e., field coil assembly, armature assembly, brushes, and ground circuit, can be tested. Using the digital multimeter, set the resistance, or ohms “Ω” scale, to the highest reading by rotating the knob on the meter. The scale may have an Omega “Ω” symbol. Place the positive or red lead on the starter motor terminal. It is the terminal protruding from the side of the yoke and attaches to the bottom large terminal of the starter solenoid. Place the black lead on the housing yoke. If a resistance reading is displayed, then the circuit indicates a complete circuit from the starter motor terminal, through the field coil windings, through the positive brush or brushes, through the armature windings, and finally through the ground brush or brushes to the yoke housing. If the resistance reading seems low, then the field coil windings may shorted to the yoke. To confirm or refute field coil windings shorted to the yoke; insulate the positive brush or brushes from the commutator by placing a piece of paper between the brush or brushes and commutator, or remove the brush or brushes from the holder or holders. Retest the circuit using the same procedure as before. If the resistance reading is still the same, then the field coils are shorted to the yoke. If the resistance reading indicates infinity ∞ or “1”, then field coils are not shorted to the yoke.
If, during the original test, the resistance reading indicates infinity ∞ or “1”, then the circuit may be open or the digital multimeter resistance, or ohms “Ω” scale, may be set too low. Try a higher scale and retest. If the results are the same, then the field coil windings may have a broken or burnt winding. To confirm or refute open field coil windings, insulate the positive brush or brushes from the commutator by placing a piece of paper between the brush or brushes and commutator or remove the brush or brushes from the holder or holders. Using the digital multimeter, set the resistance, or ohms “Ω” scale, to the highest reading by rotating the knob on the meter. Place the positive or red lead on the starter motor terminal. Place the negative or black lead on the positive brush or brushes. If the resistance reading still indicates infinity ∞ or “1”, then the field coils have an open circuit and will have to be replaced.
Field coils can be tested similarly after having been removed from the starter housing or yoke.
Place the positive or red multimeter lead on one field coil terminal. With the negative or black lead touch each of the other field leads and observe the multimeter reading on the ohms “Ω” scale. This test checks for continuity or complete circuit, or an open circuit.
To replace the field coils remove the armature from inside the starter housing or yoke. If the positive brush or brushes are part of the field coil or coils, remove the positive brush or brushes from their holders. Remove the magnetic pole screws from the outside of the starter housing or yoke. Carefully remove the magnetic pole shoes from the starter housing or yoke. Use care when removing the magnetic pole shoes, because they are fragile and may break easily. Finally carefully remove the field coils from the starter housing or yoke. Install the new field coil assembly by reversing the disassembly procedure.
If this procedure appears to be beyond the capabilities of the vehicle owner or driver, then testing and servicing the field coil assembly should be performed by a professional or ASE Master Certified mechanic. The vehicle would have to be taken to a repair shop that employs these types of mechanics such as A & M Alternator Services located at 2419 E. Jackson St. in Phoenix, Auto Electric Specialists located at 5216 W. Lamar Rd. in Glendale, Village Auto Electric Service located at 19 N. Miller St. in Mesa, All Start Electric located at 13501 E. Chandler Blvd. in Chandler, Jordan’s Automotive Specialists located at 8718 E. McDowell Rd. #3 in Scottsdale, Rob’s Quality Automotive located at 11801 N. Cave Creek Rd. in Phoenix, Scottsdale Pro Tech located at 8245 E. Butheruand Dr. #111 in Scottsdale, and Art’s Family Auto Repair located at 915 W. Hatcher Rd. in Phoenix.
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