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10-10
TROUBLE DIAGNOSIS
ELECTRICAL SYSTEMS
(286)
timing (par. 10-47), improper operation of cen-
trifugal or vacuum advance mechanism (par.
10-44), contact points improperly adjusted
(par.
10-45) worn distributor bearings or a
bent shaft, dirty or wrong heat range spark
plugs (par. 10-48). It may also be caused by
overheating, excessive carbon in cylinders, or
by low octaine fuel.
3. Overheating may be caused by one or
more of the conditions which contribute to de-
tonation, as well as by faults in engine cooling
system.
10-11 LIGHTING SYSTEM-TROUBLE
DIAGNOSIS
a. Thermo Circuit Breaker Vibrates-Lights
Flicker
When the thermo circuit breaker vibrates
and causes lights to flicker it indicates a short
in one of the lighting circuits, which may be
traced as follows:
1. Pull switch successively to each lighting
position.
If
circuit breaker vibrates in all posi-
tions except "off" the trouble should be found
in the tail lamp and license lamp
circuit.
2.
If
the circuit breaker vibrates in "park-
ing" position only, look for a short in parking
lamp circuit.
3.
If
the circuit breaker vibrates in "driv-
ing" position and is normal in all others, in-
spect headlight wiring circuit and lamp assem-
blies.
If
both filaments in headlamps burn at
same time, headlamp unit should be replaced.
4.
If
the circuit breaker vibrates with light-
ing switch in all positions, including "off" posi-
tion, the ground will be found in one of the fol-
lowing circuits: Lighting switch to stop light
switch, lighting switch to instrument panel
light switch, glove compartment light, map
light, clock, and the dome light on the Series
40. The trouble can be traced to the particular
defective circuit by removing above connections
one at a time.
If
the trouble is in the dome light circuit, the
circuit breaker will not vibrate when the six-
way connector is disconnected.
5.
If
the circuit breaker vibrates only when
the service brakes are applied, the ground will
be found in circuit from stop light switch to
rear signal lamp.
Where tracing wiring circuits refer to wir-
ing circuit diagrams in Section 10-J.
b. Lamps Fail to Burn
In general, failure of any lamp indicates a
burned out bulb, an open circuit in the wiring,
a defective switch, or a burned out fuse. See
paragraph 10-53 for test of lighting switch.
See wiring circuit diagrams in Section 10-J.
c. Lights Flare up Excessively when Engine is
Speeded Up
This condition is caused by high voltage in
electrical system due to one or more of the fol-
lowing:
1. Electrolyte in battery low or weak (par.
10-18, 10-19).
2. High r
esistance
in circuit between gen-
erator and positive post of battery due to loose
or dirty connections (par. 10-26).
3. Poor ground
between generator and
crankcase.
4. Voltage regulator adjusted too high or
inoperative (par. 10-29).
10-1 2 SIGNAL SYSTEMS-TROUBLE
DIAGNOSIS
a. Stop Lights
If
stop light fails to burn, check lamp bulb,
wiring circuit, and stop light switch. On 1949
Series 50-70, check direction signal fuse on
fuse block which also protects the stop lamp
circuit. On 1948 models the stop lamp circuit
is protected by the thermo circuit breaker on
lighting switch. See chassis wiring circuit dia-
grams in Section
10-J.
If
stop light burns when brake pedal is re-
leased, check stop light switch, also check brake
pedal clearance (par. 8-11) and check for
dragging brakes.
If
the compensating port in
brake master cylinder is plugged by foreign
material, or is covered by the piston primary
cup when brake pedal is released, high pressure
will be maintained in hydraulic system and stop
light switch will remain closed.
b. Direction Signal Lights-1948 Models.
An inoperative right indicator light may be
caused by a burned out bulb at right indicator
or a right signal lamp. The opposite applies for
inoperative left indicator light.
If
bulbs are found
okay,
look for open circuit.
See chassis
wiring
diagrams in Section
10-J.
If
signal lights are inoperative on both turns,
look for blown fuse or defective flasher.
c. Direction Signal Lights-1949 Series
50-70
An inoperative right indicator light may be
caused by a burned out left front signal lamp
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