Chevrolet 70 1969 Series, Shop Manual

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CHASSIS ELECTRICAL AND INSTRUMENTS 12-4
Figure 5 — Fuse Block and Circuit Breaker M ounting
(Conv. Cab Models) (TypicalI
cable are operating properly, replace the speed­
ometer drive gear.
To check speedometer for accuracy, use a
test machine that is equipped with a drive. Con­
nect speedometer head to drive and operate at a
known 1000 rpm. The miles-per-hour hand should
register 60 M P H and the odometer should register
one mile-per-minute. If not, speedometer head is
defective and must be replaced.
N O T E : On vehicles equipped with the front
wheel speedometer drive, refer to " F R O N T
A X L E ” (SEC. 3B) for s p e e d o m e t e r drive
components.
ELECTRIC HORN
The electric air-tone "S ” type horn is care­
fully adjusted and inspected during manufacture
and should operate indefinitely without attention.
The horn assembly should not be adjusted or re­
paired.
If the horn fails to operate, use a jumper lead
to check the external horn circuit as follows:
1. Connect jumper lead from No. 2 terminal
on horn relay to ground. If horn then operates, the
trouble is in the horn control circuit. If horn does
not operate remove jumper lead and proceed with
Step 2.
2. Momentarily connect jumper lead between
No. 3 and No. 1 terminals on horn relay. If horn
operates, the relay is defective.
3. Horn circuit is internally grounded through
the horn mounting. Therefore, it is necessary that
Figure 6 — Fuse Block and Circuit Breaker M ounting
(Tilt Cab Models) (Typical)
a good ground connection be maintained between
the horn mounting bracket and its mating part.
Check for a good ground by connecting a jumper
lead from the horn bracket to the vehicle frame or
grounded side of battery. Be sure contact is made
through the paint of the horn bracket and frame.
If trouble was not corrected by the above
checks, a foreign particle may be holding the horn
contacts open. This condition can sometimes be
corrected by energizing the horn, then lightly tap­
ping the horn power plant to dislodge the particle.
If this fails to correct the problem, replace the
horn assembly.
AIR HORN
Air horns, used as standard or optional equip­
ment on some models, are mounted on pedestals
attached to the cab roof panel. Air pressure to
horns is controlled by a control valve mounted on
the inner hinge pillar panel at left side of cab. A
signal cord is used to manually activate the con­
trol valve.
Air pressure is supplied by the pressure pro­
tection valve. Refer to "A IR B R A K E S " (SEC. 5B)
for information on the pressure protection valve.
If the air horn control valve becomes inoper­
ative, a service kit consisting of a spring, rubber
seat, and plunger may be installed after discon­
necting the air inlet line and removing end plug
from valve.
RELAYS
H O R N R E L A Y
Refer to applicable wiring diagram for wiring
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK S H O P M A N U A L