Buick LeSabre 1965 Service Manual page 637

ELECTRICAL SYSTEMS
GAS GAUGE 1 0 - 6 7
Figure 10-69—Gas Gauge
The dash unit pointer is moved
by changing the balance between
the magnetic pull of two coils in
the unit. This balance is con^
trolled by action of the tank unit
which contains a variable rheo-
stat, the value of which varies
with movement of a float and arm.
The tank unit is mounted in the
tank so that the float rises and
falls on the surface of the gaso-
line. The float is adjusted to
provide approximately 1 gallon
reserve when the dash unit point-
er is at the dot next to the "E"
position.
When the ignition switch is "On"
and the tank unit arm is in the
full position (maximum resistance
for the tan wire to ground), the
current flow to ground is through
the resistor, battery coil and the
ground coil. Due to the fact that
the ground coil has more windings
than the battery coil it builds up a
stronger magnetic field and the
dash unit pointer is pulled to the
"F" position. See Figure 10-69.
When the tank unit arm is in the
empty position (no resistance for
tan wire to ground), the current
flow is through the resistor, the
battery coil and the tan wire to
ground at the tank unit. The dash
unit pointer is thus pulled to the
"E" position.
1 0 - 5 1 GASOLINE G A U G E -
TROUBLE
DIAGNOSIS
If the gasoline gauge does not
operate properly, the dash unit,
tank unit wiring and the tank unit
should be separately tested to
determine which is at fault. The
units and wiring may be tested
by using a known good tank unit
with a 12 foot piece of red insu-
lated (#16) wire attached to bind-
ing post of unit and a similar 5
foot piece of black wire attached
to flange of unit. Attach a spring
clip to end of black wire and a
terminal to end of red wire.
1. Test of Wiring Between Dash
Unit and Tank Unit.
(a) Disconnect the tank unit tan
wire at frame side rail. This
connector is located at top of
right frame rail just forward of
gas tank on all models except
estate wagons. On estate wagons
the connector is located at the
left front corner of gas tank.
Plug the red test wire terminal
into the connector and attach the
black test wire to any convenient
ground on the car.
(b) Turn ignition switch on and
move arm of test unit up and
down against the stops while ob-
serving dash unit. If dash unit
and wiring are okay, dash unit
pointer will move freely from
"Empty" to "Full" with move-
ment of tester arm, indicating
that trouble is in tank unit or the
short wire leading to it.
(c) If, on the test of dash unit and
tank unit wiring, dash unit reads
"Empty" or noticeably low at all
times, look for a ground in the
wiring circuit between dash unit
and connector at frame rail. Also
an improper grounded dash unit
will cause unit to read low. If
dash unit reads above "Full" or
noticeably high at all times during
test, look for points of high re-
sistance or open circuit in wiring.
RESISTOR
DASH UNIT
GROUND
COIL
BODY CONNECTOR
TANK UNIT
FULL
POSITION
EMPTY
POSITION
BATTERY
COIL
TO IGNITION
SWITCH
CONNECTOR
J
Figure 10-70—Gasoline Gauge Circuit