Chevrolet 70 1969 Series, Shop Manual

Page: 502 / 913

CHASSIS ELECTRICAL AND INSTRUMENTS 12-3
pry lock on terminal clips down to assure a firm
connection when terminals are inserted into the
connector.
1. Press terminals into mating end of connec­
tor, then check to make sure terminals are firmly
engaged in connector by attempting to pull apart.
2. Connect mating ends of connector and
check to be sure all lock tangs are firmly engaged
by attempting to separate.
CHASSIS JUNCTIONS
Terminal posts on junction blocks are num­
bered; these numbers correspond with numbers
shown in chassis junction symbols on the Wiring
Diagrams.
C O N V E N T IO N A L C A B M O D E L S
The chassis junction block (fig. 3) is located
on right-hand side panel between door pillar and
back of cab. Junction block cover must be re­
moved for access to junction terminals. Refer to
applicable wiring diagram at the end of this
section for arrangement of wiring.
N O T E : On some models, the wiring junctions
are made by use of mating connectors.
T IL T C A B M O D E L S
Chassis junction block (fig. 4) is located under
left-hand step riser panel and is accessible when
left-hand door is open and cover removed. One
12-terminal junction block is used on vehicles with
standard equipment and an additional 12-terminal
junction is used when required for additional elec­
trical equipment. A 6-terminal chassis junction
block is located on the frame side rail at left side
of cab.
CIRCUIT BREAKERS A N D FUSES
Headlight and parking light circuits are pro­
tected by a 25-amp. automatic reset type circuit
breaker built into the main light switch. Any con­
dition which causes an overload on either circuit
causes the bimetallic element to open the circuit.
When element cools, the circuit breaker will close
the circuit. This off and on cycle will repeat until
light switch is turned off or until cause of over­
load has been located and corrected. Circuit break­
er is shown in main light switch wiring diagram
(fig. 17). If circuit breaker becomes defective, the
complete light switch assembly must be replaced.
A 15-amp. automatic reset type circuit break­
er is used in the two-speed axle shift switch cir­
cuit and in stop light circuit on vehicles equipped
with two-speed axle or with special I.C .C . stop
light switch. These circuit breakers (when used)
are mounted at left or right of dash panel inside
the cab.
Chassis Junction Block
Figure 4 — Chassis Junctions (Tilt Cab Models) (Typical)
The two-speed axle electric shift motor cir­
cuit is protected by an automatic reset type cir­
cuit breaker.
Any condition which causes an
overload on a circuit, such as a short, will cause
circuit breaker bimetallic element to open the
circuit; when element cools, circuit breaker will
again close the circuit. This off and on cycle will
repeat until the switch controlling the defective
circuit is turned off, or until the cause of over­
load has been located and corrected.
In the
event a circuit breaker, becomes defective (burns
out or sticks closed), the defective circuit breaker
must be replaced. Circuit breakers must be in­
stalled so the feed or battery wire is connected
to the " B A T " or short terminal, and the wires
carrying the circuit to the electrical units con­
nect to the " A U X .” or long terminal.
Figure 5 shows a typical fuse block and cir­
cuit breaker mounting on conventional cab models
and figure 6 shows a typical fuse block and cir­
cuit breaker mounting on tilt cab models. On
tilt cab models, the axle shift circuit breaker lo­
cation will vary depending on other equipment.
SPEEDOMETER
Speedometer is mechanically driven from
speedometer adapter by a flexible cable. The
miles per hour hand is magnetic cup actuated,
while the odometer is direct gear acutated. If
speedometer becomes inoperative, disconnect ca­
ble at rear of speedometer head and adapter and
check to make sure cable and drive gear on trans­
mission are operating properly. This can be done
by driving vehicle forward while an assistant
checks movement of the drive cable inside the
flexible cable.
If the drive cable and drive gear appear to be
operating properly, repair or replace the speed­
ometer head.
Replace the cable if kinked or
broken. If the speedometer head, adapter and
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L