GMC 1976 ZEO 6083 Maintenance Manual page 414

6Y- 34 ENGINE ELECTRICAL
Spark Plug Reach and Threads
Spark plugs are manufactured in a number of
thread sizes and "reaches ." Reach is the distance
from the gasket seat to the end of the shell. Spark
Plugs have a type number on the insulator which
designates plug thread size as well as the relative
position in the heat range system as previously ex-
plained .
SECONDARY IGNITION CABLES (FIGURE
32)
The secondary wiring consists of the high tension
cables connected between the distributor cap, the
spark plugs, and the high tension terminal of the
ignition coil . These cables carry the high voltage
surges to the spark plugs and are heavily insulated to
contain the high voltages . The cables are neoprene
jacketed and have a multiple cloth thread core im-
pregnated with a graphite solution to give the correct
conductivity and proper resistance for suppression of
radio and television interference .
IGNITION SWITCH
The electrical switching portion of the assembly
is separate from the key and lock cylinder . However,
both are synchronized and work in conjunction with
each other through the action of the actuator rod
assembly . For a complete explanation of the key and
lock cylinder, and the actuator rod assembly, refer to
the Steering section of this manual .
The ignition switch is key operated through the
actuator rod assembly to close the ignition primary
circuit and to energize the starting motor solenoid
for cranking . The ignition switch has five positions:
OFF, LOCK, ACCESSORY, RUN and START.
OFF is the center position of the key-lock cylinder,
and LOCK is the next position to the left . ACCES-
SORY is located one more detent to the left of
LOCK . Turning the key to the right of the OFF
position until spring pressure is felt will put the igni-
Figure 32-Secondary Wiring
tion switch in the RUN position, and when turned
fully to the right against spring pressure, the switch
will be in the START position .
In the RUN position, the ignition primary circuit
is activated through a resistance wire . The ignition
resistor wire is used in the ignition running circuit to
reduce the voltage to the ignition coil . The resistor
wire is bypassed when the engine is being started.
The purpose of this is to compensate for the drop in
voltage which occurs as the result of the heavy drain
on the battery during starting, and to provide a hot-
ter spark for starting .
All ignition switches have five terminals which
are connected in different combinations for each of
the three operating positions. A brass plate, inside
the switch, has three contacts which connect these
terminals, shows the positions of the contacts in all
positions as viewed from the key side of the switch .
There is also a ground pin in the switch which con-
tacts the "ground" terminal when the ignition switch
is in the START position . This pin contacts the IGN.
terminal when in the OFF position .
Ignition Start and Run Circuit
The ignition switch is fed from a junction at the
horn relay to the BAT. terminal of the switch . When
the ignition switch is in the OFF position, no current
flows through the switch . When the ignition switch
is turned to the ACC. position, the BAT. terminal is
connected to the ACC. terminal . This permits oper-
ation of accessories when the engine is not running.
When the ignition switch is turned to the START
position, the BAT. terminal is connected to the SOL .
and IGN . terminals. When the clutch or automatic
transmission neutral start switches are closed, cur-
rent flows to the starter solenoid . This energizes the
solenoid windings . The solenoid has two sets of
windings : a "pull-in" winding and a "hold-in" wind-
ing. Both windings are used to create the magnetic
field to actuate the solenoid plunger and move the
starter pinion into engagement with the flywheel . As
the solenoid plunger reaches the end of its travel, it
closes a switch which connects battery voltage to the
starter motor. With battery voltage applied to both
terminals of the "pull-in" windings, the "pull-in"
winding is no longer energized, so that only the
"hold-in" winding keeps the starter solenoid en-
gaged.
During cranking, current is directed from the
battery through the brass disc in the starter solenoid
housing to the "B" terminal on the solenoid and then
to the ignition coil, bypassing the ignition resistor
wire .