Cummins/Onan — Ignition Coil Testing With Ohmmeter
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Remove all attached wires from coil.
- Inspect terminals for corrosion, looseness, cracks or damage.
- Measure primary resistance between positive (+) and negative (-) terminals.
- Primary resistance should be between 3.87 and 4.73 ohms.
- Measure secondary resistance between the two high tension terminals.
- Secondary resistance should be between 12,600 and 15,400 ohms.
- Replace coil if readings are not within specifications.
Tools required
- Ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Primary 3.87-4.73 ohms
- Secondary 12,600-15,400 ohms
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.