Cummins/Onan 4.0 BF-1R/9500 — Testing Field Windings
Testing & diagnosis
For the Cummins/Onan 4.0 BF-1R/9500, from the Cummins/Onan service manual.
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Procedure
- For grounds test, disconnect all field leads and use a 120 volt series test lamp set
- Touch one prod to F1 (+) and the other to the frame; lamp should not light
- If lamp lights, field is grounded and must be replaced; test F2 lead the same way
- For open test, use an ohmmeter or 120 volt test lamp set
- Connect ohmmeter to F1 (+) and F2 (-); resistance should read 28.8 ohms (+/-3%) at 70 F
- Using test lamp set, touch prods to F1 and F2; lamp should light; if not, field winding is open
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 28.8 ohms +/-3% at 70 F
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.