Cummins/Onan — Field Windings Test
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Use continuity type test lamp.
- Disconnect and tag all field leads. Refer to wiring diagram.
- Test for open circuit by placing one test prod on each of two terminal ends.
- If lamp does not light, winding is open. If open in external lead, repair; internal break requires replacement of coil set.
- Test for ground by placing one prod on terminal end and other on bare metal frame. If lamp lights, ground indicated. Repair as necessary.
- Internal short circuit best located with sensitive ohmmeter by comparing resistance of individual coils; lower resistance indicates short. Replace entire coil set if short.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.