This air core type fuel gauge consists of three (3) copper
wire coils wound around a plastic bobbin containing a
magnet and spindle assembly. Attached to the magnet
and spindle assembly is a pointer which indicates fuel
level. The fuel gauge requires a 0 to 90 ohm resistance
sender to operate. The sender is the tank unit and
consists of a float and arm assembly and a variable
resistor. The senders resistance is controlled by the
position of float and arm assembly. A full fuel tank raises
float to its highest position. At this position the variable
resistor has a resistance of 88 ohms. With an empty fuel
tank the float assumes its lowest position, creating a
sender resistance of less than 1 ohm.
The fuel gauge circuit diagram (Figure 18) shows that
with key switch "ON," current flows from the battery
through a parallel circuit consisting of the empty coil and
the fixed resistor and thence through another circuit
- The variable resistance fuel level sender, and the
bucking coil and the full coil.
- The fuel sender only when in its empty position.
Variations in the position of the fuel level sender contact
will vary the active portion of resistance element and thus
control the amount of current flowing in the bucking and
full coils Maximum current in the bucking and full coils
occurs with the tank unit in the full "F" position. Under
this condition, the magnetic field of the bucking and full
coils is at maximum and the pointer and armature
assembly will align itself with the resultant magnetic field
of the three coils - the "Full" position. As the fuel is used,
the fuel level sender contact position changes to reduce
the current in the bucking and full coils and increases the
current in the empty coil. This variation in current
reduces the magnetic field strength of the bucking and
full coils from a maximum at "full" to zero at the empty or
"E" position at which time the armature and pointer
assembly is aligned with the magnetic field of the empty
coil. Thus, the interaction of the magnetic field of the
three coils produces a resultant magnetic field which
controls the rotation and position of the armature and
The sender and key switch terminals are connected by a
calibrating resistor (Figure 18). The other terminal is the
The sender terminal is the first terminal clockwise from
ground terminal when viewed from back side of gauge.
NOTE -The gauge Is grounded to chassis through
the ground terminal when plugged Into Instrument
cluster printed circuit.
When the key switch is turned off, pointer will not
necessarily return to the empty position. This is inherent
in the instrument and does not indicate a faulty part.
Disconnect wire at fuel tank sender unit.
Connect one lead of Gauge Tester to end of sender
wire. Connect second lead to ground. (Gauge tester
now substitutes for sender unit.
Turn key switch "ON" (Be sure there is power to
Set tester for 88 ohms. Fuel gauge should read at
full. (Pointer within boundaries of ball.
Set tester for 44 ohms. Fuel gauge should read at
half scale. (Pointer within boundaries of ball.
Set tester at 1 ohm. Fuel gauge should read at
empty. (Pointer within boundaries of ball. If fuel
gauge responds correctly to various tester settings,
gauge and wiring between gauge and sender unit
are OK. Trouble is in sender unit or sender unit is
Check sender unit ground circuit. Make sure
circuit is grounded.
If ground circuit is OK, replace sender unit If
gauge does not respond to tester:
Check continuity of gauge wiring circuits. Make
sure connector terminals are clean and tight.
Check gauge cluster ground circuit. Make sure
circuit is grounded.
If wiring is OK, replace gauge.
WATER TEMPERATURE GAUGE
The water temperature gauge circuit consists of two
basic components - the cluster-mounted gauge and the
thermistor sending unit. The sender controls the gauge
reading which indicates the water temperature. The two
units are connected electrically as shown in
The operating principle of the temperature indicating
system can be understood by reference to the
temperature gauge circuit diagram (Figure 19). With the
ignition switch closed, current will flow from the battery
through the bucking and "cold" coils and the fixed
resistor to ground, and through the "Hot" coil and the
variable resistance temperature sender to ground. The
temperature sender consists of a thermistor en-closed in
a sealed threaded shell containing a heat transfer
medium and equipped with an insulated terminal. With
the temperature sender immersed in a cold liquid
(1000F), its resistance is high and the current flowing
through the "hot" coil is small; therefore, the
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