C.E. Niehoff & Co. C633 Troubleshooting Guides - Manual (Page 4)

Page 4 TG80A
Section C: On-Vehicle OVCO Troubleshooting
OVCO Troubleshooting
Shut down vehicle and restart engine. If alternator functions normally after restart, a “no output condition” was normal
response of voltage regulator to “high voltage” condition. Inspect condition of electrical system, including loose battery
cables, both positive and negative. If battery disconnects from system, it could cause “high voltage” condition in electrical
system, causing OVCO circuit to trip.
If you have reset alternator once, and electrical system returns to normal charge voltage condition, there may have been
a one time, high voltage spike, causing OVCO circuit to trip.
If OVCO circuit repeats cutout a second time in short succession and shuts off alternator field circuit, try third restart.
If OVCO circuit repeats cutout, go to Chart 1.
Yes No
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 1.5 ± 0.2 ohms?
Yes No
Replace existing regulator with known good regulator.
Run engine. Does OVCO trip?
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)?
Chart 1 – OVCO Trip
Figure 3 – Alternator-to-Regulator 4-Socket Harness Plug
SOCKET CONNECTIONS
A F–
B Phase Signal AC
C B–
D 28 V B+
Alternator is
defective.
Alternator is
defective.
Alternator is
defective.
Original regulator
is defective.