TM 9-2320-211-20
Table 2-4. Troubleshooting-Electrical
System--Continued
Item
Malfunction
Probable Cause
Corrective Action
No.
INSTRUMENTS, GAGES
AND SENDING UNITS--Continued
23 Air pressure gage inoperative.
a. Compressed air reservoir supply
Run the engine to build up pressure
low.
to 100 psi. If the gage does not
register immediate buildup, replace
the gage (para 2-144).
Shut the petcocks
b. Air reservoir drain petcocks open.
24 Oil pressure gage inoperative.
a. Sending unit faulty
Replace the sending unit (para 2-
Replace the gage (para 2-148)
b. Gage faulty
25 Horn inoperative
Check the air pressure gage. Refer to
a. Low or no air pressure
item 22 above.
Check circuit No. 25 for continuity to
b. Electrical circuit broken. horn
system.
the horn button. Replace the horn
switch if necessary (para 2-156).
Replace the solenoid (para 2-169).
c. Defective solenoid
RADIO INTERFERENCE
SUPPRESSION
Inspect all wiring and replace it if it is
26 Interference while vehicle is in
Loose cables, bonding, or con-
nections; frayed insulation in
defective. Clean and tighten all
motion with engine not operating.
vehicle wiring.
connections.
27 Interference only when engine is
Accelerate the engine, and turn the
Generator system
running.
ignition switch off with engine at a
high speed. If the noise continues
after the switch is shut off, the
cause is in the generator system.
28 Variable pitch whining noise
Check the regulator ground cable and
a. Loose or dirty regulator con-
which varies with engine rpm.
its mounting bolts to determine if
nections.
the connections are free from dirt,
paint, or other foreign material that
could impair conductivity. Check
for tightness.
Check generator system.
b. Defective generator-regulator
capacitor.
Tighten or replace belts as necessary
c. Loose or frayed fan and drive belts.
Replace the generator (para 2-131).
29 Variable clicking noise which
Accelerate the engine and turn the
a. Ignition system
varies with engine rpm.
ignition switch off with the engine
at a high speed. If the noise stops
immediately, the cause is in the
ignition system.
Adjust the gap (para 2-121)
b.
Improper
spark plug gap
Adjust the points (para 2-122).
c.
Improper
breaker points
Replace the cables
d.
Defective
spark plug cables.
With the engine running, disconnect
e.
Defective
spark plugs
the cables from the plugs one at a
time. If the noise is reduced or
eliminated, the cause is the spark
plug. Replace the plug (para 2-12).
Check the fuel pump and electrical
f. Fuel pump
connections.
2-17. Test Equipment
2-18. L o w - V o l t a g e C i r c u i t T e s t e r
Test procedures covered in this section are based on
the use of the low-voltage circuit tester, wheeled
c i r c u i t testers (LVCT) in general use. The LVCT
v e h i c l e adapter set, adapter set. Test procedures
consists of a voltmeter, an a m m e t e r , a f i x e d
used may also be made on the vehicle using any
resistance, load bank, and field rheostat unit. They
are mounted in a metal case, which also provides
--
the required electrical range.
stowage space for the meter leads and accessories
