Guide-Matic - Cadillac 60 Series 1963 Shop Manual

12-82
ELECTRICAL SYSTEM
GUIDE-MATIC
The Power Headlamp Control (Guide-Matic)
is an electrical device that automatically controls
the headlights in response to light from an ap-
proaching car. It consists of four individual units:
a phototube unit, an amplifier unit, a power relay
unit, and a foot switch, Fig. 12-99.
The phototube unit is a single stage, light-
sensing optical device that is mounted on the top
center of the instrument panel upper cover. A
lens picks up light from approaching headlights
and focuses it on the phototube through a filter
and mask. The phototube converts the light into
an electrical signal that actuates the amplifier
unit.
The amplifier unit supplies voltage to the photo-
tube unit, and operates the power relay unit in
response to a signal from the phototube. The
amplifier is located under the instrument panel
cover, above the left side of the glove box
assembly.
The power relay unit controls the headlights in
response to the electrical impulse from the am-
plifier. It is mounted on the dash insulator, just
to the right of the parking brake assembly.
The foot switch is a special dimmer - override
type that provides either Automatic or Lower
Beam control of the headlights. It also contains
an override section for obtaining an overriding
high beam when in Automatic position.
The override section functions as follows: A
slight downward pressure on top of the switch
provides upper beam, regardless of the amount
of light on the phototube. This arrangement per-
mits signalling an approaching driver if he fails
to switch to lower beam, and also provides a
simple test for the Automatic position of the foot
switch.
A sensitivity control knob, Fig. 12-100, is lo-
cated at the back of the phototube unit. This gives
the car driver a limited range of control over
DIM and HOLD sensitivity. A detent position is
provided in the center of the control range for
normal sensitivity as adjusted at the factory.
When the control is in detent position, the knob
pointer will be pointing up.
Rotating the knob clockwise toward the word
FAR increases the sensitivity. In this position,
Guide-Matic will switch the headlights to lower
beam when an approaching car is farther away
than normal. Rotating the control counterclock-
wise, toward the word NEAR, decreases the sen-
sitivity, thus allowing an approaching car to come
nearer before switching occurs.
OPERATION-AUTOMATIC
When the light from an approaching car's head-
lights strikes the phototube unit, it is converted
into an electrical signal. This signal is then
picked up by the amplifier unit and transmitted to
the power relay unit.
A strong electrical impulse from the power
relay then causes the outer headlights to dim to
Low Beam, and cuts off power to the inner head-
lights. If the approaching car's headlights are
then switched to lower beam, the amount of light
striking the phototube unit is reduced. However,
the Guide-Matic is designed to hold the headlights
on Low Beam even with this reduction.
When the other car passes, and its lights no
longer reach the phototube unit -- the electrical
impulse no longer reaches the power relay unit.
This causes the outer headlights to return to
Upper Beam and restores current to the inner
headlights.
OPERATION-MANUAL
The Guide-Matic unit can be switched to manual
operation by rotating the control knob counter-
clockwise until the knob pointer points to OFF,
as indicated on the left side of the phototube
casting. The OFF position is obtained by opening
the circuit with an insulator at the end of the sen-
sitivity control switch. Whenever the unit is
placed in manual operation, the foot switch oper-
ates like a conventional dimmer switch.
SERVICE INFORMATION
An external 4 amp fuse is provided on the
Guide-Matic amplifier power supply, Fig. 12-99.
If this fuse should blow because of an external
short, the unit will revert to manual control and
the circuit board is protected against burning out.
In cases of Guide-Matic failures, the fuse should
always be replaced before attempting to diagnose
the condition.
103. Preliminary Checks
Before Adjustments
The Guide-Matic is adjusted at the factory and
should hold its adjustment over a long period of
time. However, loose or incorrect wiring con-
nections or even misunderstanding of the opera-
tion of the unit may lead an owner to believe that