Chevrolet DB90 Series, Service Manual

Page: 135 / 242

S ec. 6Y-129
A. C. GENERATING SYSTEM (NON-INTEGRAL TYPE)
(1) If light com es on, an open circu it e x is ts
within the regulator. R efer to regulator
te s t s la ter.
(2) If light does not com e on, leave jumper
lead connected a s shown in figure 11 and
connect a long jum per lead from generator
field "F" term in al to ground. If lamp does
not com e on, "F" term inal lead is open
circuited. If lamp does com e on, generator
field is open circu ited .
5. If indicator lamp com es on with the ignition
or control sw itch on and the engine idling, r e fe r to
"Undercharged B attery T e s t” la ter in this sectio n .
STEEL TILT CAB MODELS
WITH 1116378 REGULATOR
1. Check indicator lamp bulb.
2. V isually inspect w iring h arn ess for grounds
and poor w iring connections including connectors
at the generator and regulator.
3. If indicator lam p does not com e on with the
ignition or control sw itch in "IGN." position , and
engine not running, rem ove w iring h arness con­
n ector from regulator and connect a jumper lead
from connector-body term in al No. 4 to ground
(fig. 10).
NOTE: Make su r e jumper lead is pushed into
the connector far enough to contact the term inal
covered by the connector.
a. If the indicator lamp does not com e on,
check for an open circu it between No. 4 term inal
on regulator and the ignition or control sw itch, or
betw een the battery and jum per lead.
b. If the indicator lamp does com e on, connect
a jumper lead betw een w iring h arness connector
"F" term inal and No. 4 term inal (fig. 11). If the
indicator lamp com es on, th ere is an open circu it
within the regulator. If the indicator lamp does not
com e on, there is eith er an open in the field lead
betw een the regulator and generator or in the gen­
erator field c o il.
c. With jumper lead s till connected between
w iring h arn ess connector "F" term inal and No. 4
term in al, in se rt another jumper lead in connector-
body of generator "F" term inal and connect other
end of lead to ground on the generator. If the indi­
cator lamp does not com e on, the lead between the
regulator and generator is open. If indicator lamp
does com e on, the generator fie ld circu it is open.
4. If the indicator lamp does not go out with
the engine and generator in operation, check the
following:
a. Check generator drive belt tension a s ex­
plained under "Generator D rive Belt" p reviou sly.
b. Check for an open r e s is to r which is in p ar­
a lle l with the indicator lamp bulb a s follow s:
(1) Stop the engine; turn off a ll loads and in­
s e r t a voltm eter te st prod into the w iring
harness connector No. 4 term inal.
(2) Connect the other te st prod to ground on
regulator b a se, then turn ignition or con­
tr o l sw itch on and o b serve the voltm eter.
If voltm eter r e g is te r s le s s than 3 % v o lts,
the r e sisto r is open and if voltm eter r e g is ­
te r s over 3
% v o lts, the r e s is to r is good.
c. Connect a voltm eter between No. 3 term inal
on regulator wiring h a r n e ss connector and ground.
A zero reading in d icates an open circu it between
the battery and No. 3 regulator term inal.
d. In sert te s t prod from voltm eter into No. 2
w iring h arn ess connector term inal and the other
t e s t prod to ground on the regulator b a se. Start
engine and note voltm eter reading. If voltage read ­
ing is l e s s than 5 volts p roceed to step "e." If
voltage reading is above 5 v o lts, p roceed to step
"f."
e. Connect voltm eter between generator "R"
term in al and ground. Start the engine and ob serve
v oltm eter reading. If reading is 5 volts or m ore,
the lead between generator "R" term in al and regu ­
lator No. 2 term inal is faulty. If voltm eter reading
is le s s than 5 v o lts, r e fe r to "Voltage Regulator"
sec tio n la te r .
f. With the engine running, tem porarily ground
the regulator b ase to a known good ground. If in ­
dicator lamp goes out, clean and tighten regulator
ground connections. If indicator lamp does not go
out, the relay unit of the regulator is d efective.
5. If the indicator lamp does not go out with
the ignition or control sw itch off p roceed a s follow s:
a. D iscon n ect w iring h arn ess from generator
"F" and "R" te r m in a ls. If the indicator light goes
out, the generator has a shorted diode in the heat
sin k . If the light does not go out, connect w iring to
generator "F" and "R" term in als and rem ove w ir ­
ing h arness connector from regulator. If the indi­
cator light rem ain s on w iring leading to No. 3 and
No. 4 regulator term in als is shorted together. If
the indicator light g o es out, regulator relay points
a re stuck or there is a short between a w ire con­
taining battery voltage and the lead to No. 2 regu­
lator term in a l. P ro ceed to step "b."
b. If indicator light does not go out with w ir ­
ing disconnected from the regulator, connect a
v oltm eter between No. 2 term inal of regulator
w iring h arn ess connector and ground. Any voltage
reading in d icates a shorted condition in the w iring.
No voltage reading in d icates a stuck relay unit.
STEEL TILT CAB MODELS
WITH 9000590 REGULATOR
1. Check indicator lamp bulb which may be
burned out.
2. V isu ally inspect w iring h arness for grounds
and w iring connections including connectors at
gen erator and regulator.
3. If indicator lamp does not illum inate with
ignition or control sw itch on and engine not running,
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT