(6) Steps (3, 4 or 5) above will confirm system op-
eration. Indicator light illumination means that
there is power available at the output of the relay
only, and does not necessarily verify system opera-
tion.
(7) If turning the switch ON produced no distinct
current draw on the ammeter the problem should be
isolated in the following manner:
(a) Confirm the ignition switch is ON.
(b) Ensure that the heated rear glass feed wire is
connected to the terminal or pigtail and that the
ground wire is in fact grounded.
(c) Ensure that the fusible link and control cir-
cuit fuse is operational and all electrical connec-
tions are secure.
(8) When the above steps have been completed and
the system is still inoperative, one or more of the fol-
lowing is defective:
(a) Control switch/timer relay module.
(b) All rear window grid lines would have to be
broken or one of the feed wires are not connected
for the system to be inoperative.
(9) If turning the switch ON produces severe volt-
meter
deflection,
the
circuit
should
be
closely
checked for a shorting condition.
(10) If the system operation has been verified but
indicator lamp does not light, replace the switch.
(11) For detailed wiring information, refer to group
8W, Wiring Diagrams.
GRID TEST
The horizontal grid lines and vertical bus bar lines
printed and fired on inside surface of rear window
glass (Fig. 2) comprise an electrical parallel circuit.
The electrically conductive lines are composed of a
silver-ceramic material which when fired on glass be-
comes bonded to the glass and is highly resistant to
abrasion. It is possible, however, that a break may
occur in an individual grid line resulting in no cur-
rent flow through the line. To detect breaks in grid
lines the following procedure is required:
(1) Turn ignition ON and turn control switch to
ON. The indicator light should come on.
(2) Using a DC voltmeter with 0-15 volt range,
contact terminal B with negative lead of voltmeter.
With positive lead of voltmeter, contact terminal A
(Fig. 2). The voltmeter should read 10-14 volts. A
lower voltage reading indicates a poor ground con-
nection.
(3) With negative lead of voltmeter, contact a good
body ground point. The voltage reading should not
change.
(4) Connect negative lead of voltmeter to terminal
B and touch each grid line at Mid-Point with Posi-
tive lead. A reading of approximately 6 volts indi-
cates a line is good. A reading of 0 volts indicates a
break in line between Mid-Point C and terminal A.
A reading of 10-14 volts indicates a break between
Mid-Point C and terminal B. Move toward break and
voltage will change as soon as break is crossed (Figs.
2 and 3).
CONTROL SWITCH/TIMER RELAY 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 the switch, relay assembly from the in-
strument panel or console, see Group 8E, Instrument
Panel and leave the switch connector plugged in.
(2) Turn ignition ON.
(3) Using a DC voltmeter, with 0-15 range, check
voltage at terminals B, I and L. (Figs. 3 and 4). Ter-
minals B and I should confirm a voltage of 10 to 14
volts to ground when the ON switch is pressed. Ter-
minal L should confirm voltage to ground. When ter-
minals B and I show no voltage, trace circuit
upstream of switch/relay module for problem (wiring
cut, fusible link or circuit breaker inoperative, bulk-
head connector not operative, etc.) If terminal L in-
dicates voltage, place switch in Off position. If
voltage at L is still indicated or indicator lamp re-
mains on, the switch/relay module should be re-
placed.
(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.
Fig. 3 Systems Electrical Circuit
8N - 2
REAR WINDOW DEFOGGER
Ä