C.E. Niehoff & Co. N1246-1 Troubleshooting Guides - Manual (Page 4)

Page 4
TG0049A
Section 3: Advanced Troubleshooting
Shut off engine. With key off, engine off: Test for battery voltage at alternator 28 V B+
terminal. Does battery voltage exist?
Yes No
Repair vehicle ignition circuit wiring as necessary. Continue test.
Chart 1 – No 28V Alternator Output – Test Charging Circuit
With DMM, check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator
harness plug. Connect black lead to B+ terminal on alternator. Does meter show 1.8 to 2.2 ohms?
Yes No
STATIC TEST – KEY ON, ENGINE OFF
T
T
Yes
Test phase signal into regulator (AC). Set meter to diode tester:
Connect red lead of DMM to socket G of regulator harness and
black lead to socket E. Meter should show voltage drop value.
Then reverse meter lead connections. Meter should show OL
(blocking).
No
T
T
Shut down vehicle and restart engine. Does alternator function normally after restart?
Yes No
T
T
Regulator responded to overvoltage condition.
Go to Chart 3 on page 6 to troubleshoot OVCO.
Figure 3 – Alternator-to-Regulator
Harness Plug
With key on, engine running: Test for battery voltage between IGN terminal on regulator and alternator
B– terminal. Does 28 V battery voltage exist?
Yes No
T T
T
Alternator is defective.
T
Alternator is defective.
T
Alternator is defective.
T
Regulator is defective.
Yes
Connect jumper wire from socket A in regulator harness plug to B– terminal
on alternator. Spark will occur. Touch steel tool to shaft to detect significant
magnetism. Is shaft magnetized?
No
T
T
Repair vehicle ignition circuit wiring as necessary. Continue test.
Yes No
T T
SOCKET CONNECTIONS
A ° F–
B ° AC1
C ° Not used
D ° B+
E ° P
F ° AC2
G ° B–
H ° B–
I ° AC3
With key off, engine off: Disconnect alternator-to-regulator harness from regulator. Test for battery voltage
across sockets D and G in harness plug. Does 28 V battery voltage exist?