C.E. Niehoff & Co. N1601/N1602/N1603/N1604 Troubleshooting Guides - Manual (Page 8)

Page 8 TG29D
Section C: Advanced Troubleshooting
(CONT’D)
Yes No
Alternator is defective.
Unplug alternator-to-regulator 4-socket harness from regulator. Connect red lead from DMM to socket A in plug.
Connect black lead to socket D in plug. Does resistance read 1.0 ± 0.2 ohms?
Chart 3b – N3107, N3118, N3211, N3223, N3237, N3245 – No 28 V Alternator Output – Test OVCO Circuit
(28V LED on N3223 steady RED)
Yes No
Replace existing regulator with known good regulator.
Run engine. Does OVCO trip?
Alternator is defective. Original regulator is
defective.
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Chart 3a – N3118, N3223 – No 14 V Alternator Output – Test OVCO Circuit (14 V LED on N3223 steady RED)
Yes No
With red lead from DMM connected to socket A in plug, connect black lead to B– terminal.
Does resistance read OL (out of limits)?
Alternator is defective.

Chart 3 – N3107, N3118, N3211, N3223, N3237, N3245 – OVCO Trip – Determine 28 V or 14 V
(LEDs on N3223 will determine affected output)
Yes No
28 V side tripped OVCO circuit.
Go to Chart 3b.
With meter red lead on 28 V B+ at battery and black lead on chassis ground, start engine.
Watch meter dial: Does meter read charge voltage above 29 V?

14 V side tripped OVCO circuit.
Go to Chart 3a.
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Figure 8 – Alternator-to-Regulator 4-Socket
Harness Plug
SOCKET CONNECTIONS
A F–
B Phase Signal AC
C B–
D 28 V B+
Yes No
Original regulator
is defective.
Replace regulator with known good regulator. Run
engine. Does OVCO trip?
Alternator is
defective.
 
Yes No
Alternator is defective.
Unplug alternator-to-regulator 4-socket harness from regulator. At receptacle on regulator, connect red lead from
DMM to socket C. Connect black lead to B– terminal. Does resistance read OL (out of limits)?
 