Chevrolet 70 1969 Series, Shop Manual

Page: 500 / 913

SECTION 12
CHASSIS ELECTRICAL AND INSTRUMENTS
This group, covering maintenance of chassis electrical system
and units, is divided into sections as shown in the index following.
Section Page No.
Miscellaneous Electrical........................................................... 12-1
Alarm System.............................................................................. 12-5
Instruments and G a u g e s ........................................................... 12-5
Lighting System........................................................................... 12-9
Wiring D i a g r a m s ................................................... 12-17
MISCELLANEOUS ELECTRICAL
N O T E : Certain electrical units, when closely
associated with some other system or unit, are
covered in other sections of this manual.
W IR IN G D IAG RA M S
Wiring diagrams, covered at the end of this
section, show electrical circuits and connections
for standard and optional equipment used on truck
series covered by this manual. Standard equip­
ment is shown in solid lines on diagrams and
optional equipment is shown in broken lines.
Truck series to which each diagram applies is
shown on each diagram.
HARNESSES A N D WIRES
Some wires are grouped and taped together
with a moisture and heat resistance black, plastic
type tape to form a wiring harness; in other in­
stances a single wire or cable is used to complete
the circuit.
Connections between chassis wiring harness
and the engine, body, and lighting wiring harnesses
are made through a terminal post-type chassis
junction b l o c k or through multiple plug and
receptacle-type connectors at engine side of dash.
Instrument cluster wiring connections are
made through multiple plug and receptacle-type
connectors and screw-type terminals. Electrical
connections at other electrical units and controls
are made through plastic insulated blade-type con­
nectors or screw-type terminals.
Every wire is of a specific size with plain
colored or striped plastic insulation as indi­
cated on the wiring diagrams. Insulation colors
assist in tracing circuits and in making proper
connections.
On vehicles equipped with the V-6 gasoline
engine, a 1.52 ohm resistance wire is used in the
engine wiring harness to connect the ’T G N " term­
inal of the ignition switch to the positive (+)
terminal of the ignition coil. The proper length
wire is used to provide the correct resistance.
F U SIB LE LIN K
A fusible link system is incorporated in the
wiring harness to protect all feeds which are not
otherwise protected by fuses or circuit breakers.
The fusible link consists of a ware which is four
gauge sizes smaller than the smallest feed wire.
For example: a fusible link of 16 gauge wire must
have 12 gauge wire or larger in all unprotected
circuits of the link system.
The fusible links are located outside the wir­
ing harness wrap. To aid in identification, the
gauge size of the wire is labeled on the side of
each link in three places.
IM P O R T A N T : If an overload or some other
condition destroys the link, locate and correct
the cause of trouble, then replace the link with a
wire of the same gauge size and length.
FUSE BLOCKS A N D FUSES
A bulkhead fuse panel provides power take­
offs and fuse clips for appropriate circuits. The
engine wiring harness connectors are bolted to the
fuse panel.
On some models, two 4-ampere fuses are
used to protect the ammeter. These fuses are
located on fire wall near fusible links.
On some models, one or more replaceable
fusible links are located on the fire wall and are
connected into major wiring harness feed circuits.
The fusible links are incorporated as part of the
wiring system to provide increased overload pro­
tection to electrical circuits, except the starting
motor circuit, which are not otherwise protected
by fuses.
CHEVROl ET SERIES 70-80 HEAVY DUTY TRUCK SHOP MANUAL