C.E. Niehoff & Co. N1241-1 Troubleshooting Guides User Manual
Page 6
Page 6
TG0043B
(CONT’D)
Section 3: Advanced Troubleshooting
Yes
No
Alternator is defective.
Unplug alternator-to-regulator harness from regulator. Connect red lead from DMM to socket A in plug.
Connect black lead to socket D in plug. Does resistance read 1.4 ± 0.2 ohms?
Chart 3
– 28 V LED Steady RED– No Alternator Output – Test OVCO Circuit
Yes
No
Reconnect cables. Replace existing regulator with known
good regulator. Run engine. Does OVCO trip?
Alternator is defective.
Original regulator is defective.
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Yes
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Original regulator is defective.
Replace regulator with known good regulator. Run engine. Does OVCO trip?
Chart 4
– 14 V LED Steady RED– No Alternator Output – Test OVCO Circuit
Alternator is defective.
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Remove 28 V and 14 V positive battery cables AT BATTERY PACK before proceeding.
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Set DMM to
manual ohms scale. Connect red lead from DMM to socket A in plug. Connect black lead to
B– terminal. Does meter read OL (out of limits)? Then connect red lead to socket D and black lead to B–
terminal. Does meter read OL (out of limits)?
Alternator is defective.
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No
Go to Chart 3.
Run engine. Is 28 V LED on regulator flashing GREEN?
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Yes
No
With engine off, is battery voltage present at alternator 14 V B+ terminal?
Chart 2 – 14 V LED Flashing AMBER – No 14 V Alternator Output – Test Circuit
Yes
No
Connect DMM red lead to pin E on alternator-to-regulator harness plug.
Connect black lead to pin C on same plug. Does battery voltage exist?
Alternator is defective.
Repair vehicle wiring
as necessary. Continue test.
TTTTT
TTTTT
Substitute a known good regulator. Run engine. Is regulator setpoint voltage present and is 14 V LED flashing GREEN?
Yes
No
Original regulator was defective.
TTTTT
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Yes
No
Go to Chart 1.
Run engine. Is 28 V LED on regulator flashing GREEN?
TTTTT
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Alternator is defective.
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