Chevrolet 1977 light duty truck, Service Manual

Page: 803 / 861

A L IG N IN G PIN
Fig. 8-16--W asher M echanism M ou n tin g on W iper
Figure 8-16 shows the assembly o f the washer pu m p
to the wiper motor.
ELEC TR IC A L C IR C U IT S
T h e following facts should be kept in m ind
th roughout the following explanation.
1. The wiper dash switch is a grounding type
switch, and therefore must be securely mounted.
2. W hen installed in a vehicle, the wiper motor is
connected to the chassis through a ground strap. This in
effect connects the wiper housing to the ground side o f
the battery.
3. The ignition switch opens and closes the feed
wire circuit to the wiper. Therefore, it must be turned
O N to operate wipers.
The wiper m otor operation is controlled by two
switches—a dash control switch and a p ark in g switch
located in the w iper m otor gear box.
The p ark in g switch contacts are normally closed and
are opened by a cam on the gear w hen the wiper blades
reach the park position. The park switch acts as a
holding switch to m a in ta in the motor circuits to ground
d u rin g that period o f operation between the time the
o p e ra to r turns the wiper off at the dash switch and the
blades reach the park position. Figure 8-17 shows the
park switch contact open.
" L o " Speed Operation
W h e n the o p erato r turns the w iper dash switch to
the " L O ” speed position, the w iper m otor circuits are
com pleted to ground at the d ash switch as follows:
(R efer to Figure 8-18). C u rre n t flows from the battery
through the ignition switch to the center term inal of the
wiper term inal board. F rom the center terminal, current
then passes through the black with pink stripe lead to the
series field coils (L arger d ia m e te r wire) where it divides
and flows as follows:
1. The shunt field coils to wiper term inal No. 3
through the w iring harness to the dash switch to ground.
Fig. 8 1 7 - Gear in PARK Position—Contacts Open
2. The series' field-armature circuit is completed via
w iper terminal No. 1 through the w iring harness to the
dash switch to ground.
" H I " Speed Operation
Turning the w iper dash switch to the " H I " or fast
speed position changes the shunt field coil circuit as
follows: (R efer to Figure 8-19).
With the dash switch in the HI speed position, the
shunt field coil current passes through a 20 o h m resistor
on the back o f the wiper terminal board to term inal No.
1 and then via the w iring harness to the dash switch to
ground. The arm a tu re and series field circuit is also
completed via the w iring harness from wiper terminal
No. 1 to the dash switch to ground.
Turning the W iper " O F F "
Turning the w iper dash switch to the O F F position
opens the wiper circuits to ground at the dash switch. If,
however, the w iper blades are in any position other than
the normal park or off position, the wiper m otor circuits
are completed to g ro u n d by the w iper m otor park switch
as follows: (R efer to Figure 8-20).
1. The series field-armature circuit is completed to
ground via the p ark in g switch to the wiper housing to
chassis o f vehicle.
2. The shunt field coil circuit is completed to
ground via wiper term inal No. 3 through the wiring
harness to the dash w iring harness to wiper terminal No.
1, through the park in g switch to ground.
IM P O R T A N T : Note that the shunt field
circuit during the parking operation bypasses
the resistor causing the w iper to operate in
PARK SWITCH
(CONTACTS OPENED
BY CAM)