Cummins/Onan — Generator Tests
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Temporarily disconnect two generator ac leads from exciter terminals E1 and E2.
- Connect another source of ac power of proper voltage to E1 and E2.
- If no dc voltage across terminals AF1 (+) and AF2 (-), exciter is not functioning.
- If dc voltage at AF1 and AF2 is 25 volts or higher with no load but no ac output, check alternator for ground, open, etc.
- No terminal of exciter should show grounded circuit.
- If ac voltage drops under load, test exciter rectifiers with ohmmeter.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 25 volts dc
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.