GMC 4000 Series Service Manual page 32

SHUNT W IN D IN G
SERIES W IN D IN G
WIPER TERMINAL BOARD
M O T O R U N IT
PARKING SWITCH
CO N TACTS
through the series field coil and divides; part
passing through the shunt field coil to ground at
the dash switch, the remaining part passing through
the armature to ground at the dash switch.
High Speed Operation
Moving the dash switch to "HIGH" speed p osi­
tion opens the shunt field circuit to ground at dash
switch and keeps the armature circuit closed to
ground. The shunt field current must then pass
through a resistor located on the wiper terminal
board, and then through the same lead that connects
the armature circuit to ground through the dash
switch.
Parking Circuit
When wiper is turned off, circuit is broken at
the dash switch. However, current from battery
continues to flow through motor, through the park­
ing switch contacts to ground. When wiper blades
reach "PARK" position at the inboard end of wiper
pattern, the parking switch contacts open, stopping
the motor.
TROUBLESHOOTING WIPER MOTOR
Refer to figures 9, 10, and 11 when trouble­
shooting two-speed wiper.
TYPICAL TROUBLE CONDITIONS
1. Wiper will not shut off.
2. Wiper inoperative.
3. Wiper has one speed (HIGH).
4. Wiper has one speed (LOW) and shuts off
with dash switch in "HIGH" position.
G M C S E R V I C E M A N U A L
# 3 TERMINAL
# 1 TERMINAL
# 2 TERMINAL
D A S H SW ITC H
BATTERY
Figure 9 — Wiper Motor and W asher W iring Diagram
when wiper is turned "OFF."
tion but too fast in "HIGH" speed position.
CHECKING INSTALLED WIPER
Wiper Will Not Shut Off
and "LOW" speeds, "LOW" speed only, or "HIGH"
speed only.
speed during parking cycle.
motor and try operating wiper independently of the
dash switch as shown in figure 11. If wiper oper­
ates correctly independently of the dash switch
(shuts off correctly with crank arm in "PARK"
position) refer to possible causes below:
tween wiper terminal No. 1 and dash switch is
grounded, or the dash switch is defective.
lead between wiper terminal No. 3 and dash switch
is grounded, or the dash switch is defective.
lead between wiper terminal and dash switch is
open, or the dash switch is defective.
remove it from cab, then remove covering from
over drive gears and check parking switch contacts
which may be broken or stuck in closed position;
check for a grounded lead at No. 1 or 3 terminals
(fig. 11), or for a grounded shunt field.
GENERAL MAINTENANCE
W A S H E R U N IT
5. Blades do not return to "PARK" position
6. Wiper speed normal in "LOW" speed p osi­
7. Wiper operates intermittently.
1. Determine if wiper operates in both "HIGH"
IMPORTANT: Wiper must operate in "LOW"
2. Disconnect the wiring harness from wiper
a. If wiper operates in both speeds, lead be­
b. If wiper operates in "LOW" speed only, the
c. If wiper operates in "HIGH" speed only, the
3. If wiper still fails to operate correctly,
Sec. 1
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T-5827