GMC T Series 1994 Repair Manual page 604

Figure 1— CS-144 Generator
Both the " L" and " I" terminals serve to turn on the
regulator and allow field current to flow when the switch
is closed. The " I" terminal may be connected either
directly to the switch, or through a resistor. The " I"
circuit may be used with or without anything connected
to the " L" circuit.
GENERATOR O U TPU T TEST
This test requires a both standard test stand to oper­
ate the generator, and a fully charged battery.
1. Install and connect the generator to the test stand
as shown in figure 3. The carbon pile must be
turned off to begin the test. Be sure that the gener­
ator BAT terminal is connected to the battery posi­
tive terminal (through the ammeter) and that the
battery and generator are properly grounded.
2. Connect a 30 to 500-ohm resistor between the
positive battery terminal and the " L" terminal on the
generator.
DIAGNOSIS
3. Operate the generator through the test stand,
increasing speed slowly, and observe the voltage.
4. If the voltage is uncontrolled and increases above
16 volts, the rotor field is shorted, the regulator is
not working properly, or both. A shorted rotor field
coil can cause problems in the regulator.
5. If the voltage is below 16 volts, increase speed and
adjust the carbon pile to obtain maximum amper­
age output. Maintain the voltage above 13 volts.
6. If the output is within 15 amperes of the rated out­
put, the generator is good.
7. If the output is not within 15 amperes of the rated
output, replace the generator.
Figure 2— Generator Schematic
F7080