C3, TM 9-2320-211-20
NOTE
CAUTION
If a lower than battery voltage, or a zero
Do not connect the ohmmeter to the ignition
voltage reading is indicated, check the circuit
circuit and turn the ignition switch to ON
for loose or broken connections. Repair as
since ohmmeter will be damaged.
required.
c. Connect positive (+) lead of ohmmeter to the
sending unit and negative (-) lead of ohmmeter to vehicle
ground (fig. 2-34).
ground and contact case of gage (fig. 2-34). Voltmeter
should indicate battery voltage.
(1) Temperature gage sending unit.
NOTE
(a) If ohmmeter indicates a zero reading when
This check (f above) is important. If case of
engine is cold, replace sending unit. The sending unit
gage is not properly grounded, gage will not
should indicate a high resistance.
operate.
(b) Start engine. The ohmmeter will indicate a
lower reading as engine is warming up.
g, Turn ignition switch to OFF.
(c) Stop engine. The ohmmeter will indicate a
high reading as engine is cooling.
switch-to-gage wire and connect wire to gage.
(d) Replace sending unit if readings are not as
i. Disconnect wire from gage to sending unit at the
indicated in (b) and (c) above.
gage.
(2) Oil pressure gage sending unit.
j. Connect a suitable jumper wire to sending unit side
(a) The ohmmeter should indicate a 0- to 1-ohm
of gage.
k. Connect one lead of field rheostat to jumper wire
reading with engine stopped; if ohmmeter does not
indicate this reading, or exceeds 1 ohm, replace sending
from gage, and the other field rheostat wire to vehicle
ground (fig. 2-34).
unit.
(b) Start engine. The ohmmeter should indicate a
1. Turn ignition switch ON.
m. Turn field control knob and watch gage. The oil
higher reading (10 to 40 ohms); if a higher reading is not
pressure and fuel gage should go from zero to full scale if
indicated, replace sending unit.
operating correctly. Using a 13- to 15-ohm resistance,
(3) Fuel gage sending unit.
gage should read scale.
(a) Check for ground between fuel tank and
NOTE
vehicle with ohmmeter. A zero reading should be
obtained. If fuel tank is not grounded to vehicle, the
This check (m above) will not check the
sending unit will not operate.
(b) The ohmmeter should indicate a reading
temperature gage, since it is a high resistance
gage.
between 0 and 40 ohms, depending on the amount of fuel
in the tank. If ohmmeter indicates a reading higher than
n. To check temperature gage, ground one end of
j u m p e r wire from gage to vehicle ground. The
40 ohms, replace sending unit.
(c) The ohmmeter should indicate a higher
temperature gage should read high temperature when
reading as fuel tank is filled and a lower reading as fuel is
grounded, and zero temperature when jumper is not
grounded (fig. 2-34).
withdrawn. If sending unit does not conform to this test,
replace sending unit.
o. Turn ignition switch to OFF.
(d) To test inaccessible sending units and the
p. Remove jumper wire from gage and connect wire
electrical wire from gage to sending unit, omit procedure
from sending unit to the gage.
in (b) and (c) above, and proceed as follows:
q. Disconnect wire from sending unit to gage at the
1. Disconnect wire from gage to sending unit at
sending unit (fig. 2-34).
r. Turn ignition switch to ON.
the gage.
2. Connect positive (+) lead of ohmmeter to
s. Make the same checks as in e and n above. If gage
does not conform to the readings outlined, repair or
wire from sending unit and the ohmmeter negative (-)
lead to vehicle ground.
replace wire from gage to sending unit.
3. Follow procedures outlined in (3)(a) through
r. Turn ignition switch to OFF. Connect wire from
(3)(c) above for sending unit being tested.
gage to sending unit.
NOTE
Electrical gages indicate an approximate
reading; for accurate readings, use master
gages connected to the circuit being tested.
a. To test functioning of the sending units, an
ohmmeter with a 0- to 7,000-ohm range is recommended.
The following procedure applies to any sending unit being
tested.
b. Disconnect wire from gage-to-sending unit at the
sending unit.
