Chevrolet 70 Series 1970, Service Manual

Page: 761 / 841

CHASSIS ELECTRICAL AND INSTRUMENTS 12-15
ENGINE BRAKE SWITCH
(WHEN USED)
Three sw itch es, connected in s e r ie s , are used
to operate the engine brake sy stem . The m anually-
operated engine brake sw itch on con sole i s fed
from No. 10 cir cu it breaker on a c c e sso r y bus bar
when engine control sw itch and engine brake sw itch
a re in "ON" position . A lso , th ere must be a clo sed
c ircu it through sw itch at clutch lev er and m icro
sw itch at buffer sc r e w to supply current to s o le ­
noid va lv es at brake supply housings.
R efer to "Engine B rak e” under "IN-VEHICLE
SERVICE” in 71 SERIES DIESEL ENGINES (SEC.
6
C) of th is manual for inform ation pertaining to the
engine brake.
INTER-AXLE DIFFERENTIAL
LOCK SWITCH
The in te r -a x le differential lock sw itch is lo ­
cated on the dash panel or con sole on v eh icles
ALARM
V arious alarm s y s te m s are used on v eh icles
cov ered by th is manual. T e ll-ta le lig h ts, located
on the gauge and t e ll- t a le panel in front of driver
a re illum inated only when the bulb behind the le t­
terin g is illum inated.
A low vacuum , low a ir p r e s s u r e , an d /or engine
alarm buzzer is u sed to audibly a ler t the driver of
low vacuum, low a ir p r e ssu r e , low o il p r e ssu r e ,
o r an overheated engine.
LOW VACUUM ALARM SYSTEM
The low vacuum alarm sy stem , on v e h ic le s so
equipped, c o n sists of a low vacuum sw itch, a b u zzer,
and a gauge to audibly and visu ally warn the driver
when vacuum in the sy ste m is below a sa fe lim it.
The low vacuum a la rm b uzzer is mounted on
left sid e of dash panel in sid e the cab. When circu it
through buzzer is com pleted at low vacuum sw itch,
action of the vibrating arm ature strik in g the core
produces a buzzing sound.
Low vacuum alarm sy ste m w iring connections
are shown on wiring diagram s in applicable "Wiring
D iagram s" booklet. The alarm buzzer and sw itch
a re not repairable u n its. If unit b ecom es inoper­
a tiv e, rep la ce.
LOW AIR PRESSURE ALARM SYSTEM
The low air p r e s s u r e alarm sy ste m , on v e ­
h ic le s so equipped, c o n sists of a low air p r essu r e
equipped with the tandem rea r a x le. When sw itch
le v e r is position ed in "LOCK"position, the "DIFF.
LOCK" te ll- t a le lamp illu m in a tes. R efer to "REAR
AXLE AND CONTROLS" (SEC. 4A) of th is manual
for inform ation rela tiv e to th is unit.
FUEL SHUT-OFF SOLENOID
An engine fuel sh u t-o ff solen oid is used to
control the flow of fuel to the engine. The solen oid
is en ergized through No.
8
circu it breaker on a c ­
c e s s o r y bus bar when control sw itch is in "IGN"
or "ACC" position.
NOTE: On S e r ie s H N /JN -90, the solen oid is
en ergized from "IGN" p osition of the control
sw itch.
IMPORTANT: F eed w ire to fuel sh u t-off s o le ­
noid must be connected to the low er (long) term inal
on solen oid (fig. 14). If feed w ire is connected to
the upper (short) term in al, damage to w iring har­
n e s s e s and control sw itch w ill resu lt when control
sw itch is energized.
SYSTEM
sw itch, a b u zzer, and a t e ll- ta le an d /or gauge to
audibly and v isu a lly warn the driver when air
p r e s s u r e in the sy ste m is below a sa fe lim it for
brake operation. R efer to "AIRBRAKES" (SEC. 5B)
of this manual for inform ation on low air p r e ssu r e
sw itch.
The low air p r e ssu r e alarm buzzer is mounted
on left sid e of dash panel in sid e the cab on conven­
tional cab m odels; on instrum ent panel to steerin g
colum n support b racket on 70-80 tilt cab m odels;
or under the con sole (fig. 7) on alum tilt cab
m o d els. When c ir c u it through b u zzer i s com ­
p leted at low air p r e ssu r e sw itch, action of the
vibrating arm ature strik in g the core prod u ces a
buzzing sound.
Low air p r e s s u r e alarm sy ste m w iring con­
nections are shown on applicable w iring d iagram s.
In the event of fa ilu re, the buzzer m ust be replaced.
NOTE: T his sy ste m is part of the "Engine
A larm System " when veh icle is so equipped.
ENGINE ALARM SYSTEM
This sy ste m , used a s optional equipment on
som e v e h ic le s, audibly and visu ally w arns the
driver of Low A ir P r e s s u r e , Low Oil P r e s s u r e ,
and O verheated Engine or L o ss of Coolant. The
alarm sy ste m c o n sists of a low air p r e ssu r e
sw itch , low o il p r e ssu r e sw itch, hot engine sw itch
an d /or low coolant probe, alarm buzzer and r e c ti­
fie r assem b ly , low coolant control, and a sep arate
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL