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8N - 2
REAR WINDOW DEFOGGER
•
(b) Rear window grid lines (all grid lines would
have to be broken) or one of the feed wires are not
connected for the system to be inoperative.
The following paragraphs outline component check
out procedures.
If turning the switch ON produces severe voltmeter
deflection, t h e circuit should be closely checked for a
shorting condition.
If system operation has been verified but indicator
bulb does not light, check and replace bulb.
For detailed wiring information, refer to Group 8W
- Wiring Diagrams.
REAR WINDOW GRID LINES TEST
Horizontal grid lines and vertical bus bar lines
printed and baked on inside surface of rear window
glass (Fig. 1) comprise an electrical parallel circuit.
The electrically conductive lines are made of a silver-
ceramic material. When baked onto glass they be
come bonded to the glass and are highly resistant to
abrasion. It is possible, however, t h a t a break may
exist or occur in an individual grid line resulting in
no current flow through the line. To detect breaks in
grid lines, the following procedure is required:
(1) Turn ignition on and push control switch to
ON. Indicator light should come on.
(2) Contact negative lead of a DC voltmeter, to
vertical bus bar connecting grid lines on passenger
side of vehicle (point A of Fig. 1). Contact positive
lead of voltmeter, to vertical bus bar on driver side of
vehicle (point B of Fig. 1). Voltmeter should read
10-14 volts.
(3) With negative lead of voltmeter, contact a good
body ground point. Voltage reading should
not
change. A different reading indicates a poor ground
connection.
(4) Connect negative lead of voltmeter to Point A
on passenger side bus bar and touch each grid line at
Mid-Point with positive lead. A reading of approxi
mately 6 volts indicates a line is good. A reading of 0
volts indicates a break in line between Mid-Point C
and Point B. A reading of 10-14 volts indicates a
break between Mid-Point C and ground Point A.
Move toward break and voltage will change as soon
as break is crossed.
CONTROL SWITCH/TIMER MODULE TEST
Control switch/timer relay module may be tested
in-vehicle or bench tested. In vehicle testing is ac
complished in the following manner:
(1) Remove switch from instrument panel (refer to
Control Switch Replacement) and leave switch con
nector plugged in.
(2) Turn ignition ON.
(3) Using a DC voltmeter, check voltage at termi
nals B, I and L (Figs. 2 and 3). Terminals B and I
should confirm a voltage of 10 to 14 volts to ground.
Terminal L should confirm 0 volts to ground. When
terminals B and I show no voltage, trace circuit up
stream of switch/relay module for cause:
• wiring cut
• fusible link faulty
• circuit breaker inoperative
• bulkhead connection bad, etc.
If terminal L indicates voltage, place switch in
OFF position. If voltage at L is still indicated or in
dicator lamp remains on, switch/relay module should
be replaced.
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Fig. 2 Systems Electrical Circuit
J 9 2 8 N - 5
(4) If the relay checks out to this point, momen
tarily operate switch to ON position. The indicator
lamp should come on and remain on for approxi
mately 10 minutes. Terminal L should confirm volt
age. If the indicator lamp fails to light or voltage at
terminal L is not confirmed the switch/relay module
should be replaced.
Bench checking of the relay may be accomplished
in the following manner. By following the in-vehicle
procedure except Step 2: With a DC power supply,
apply 12 volts to terminal B and I and ground termi
nal G.
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