4-26 4203781 First Edition
ELECTRICAL
4
Glow Plug Circuit—Theory of
Operation
Unswitched Power Circuit
Unswitched power is available from the battery positive
terminal to the starter motor battery terminal and then
from the starter motor battery terminal to 50-amp circuit
breaker (F1) battery terminal. Unswitched power is
available through the 50-amp circuit breaker (F1) to
10-amp circuit breaker (F5).
Unswitched power is provided from 10-amp circuit
breaker (F5) to PTO switch terminal E.
Unswitched power is also available from the starter motor
battery positive terminal to the battery terminal of 50-amp
circuit breaker (F3). Circuit breaker (F3) provides
unswitched power to glow plug relay battery terminal.
Interlock Circuit
The interlock circuit provides 12 volts to the key switch.
The following must occur before the key switch is
provided with 12 volts:
• PTO switch in the off position
• Park brake switch in the on position
With the PTO switch in the off position and park brake
switch in the on position, voltage is provided from the
park brake switch to key switch terminal B.
Glow Plug Circuit
Key switch terminal B provides voltage to the glow plug
switch. When the glow plug switch is held in the on
position, voltage is provided to the glow plug solenoid
positive terminal, energizing the solenoid. With the
solenoid energized, voltage is provided through 50-amp
circuit breaker (F3) and the glow plug solenoid contacts
to the glow plugs, heating the glow plugs. Voltage is also
provided from the glow plug switch to the glow plug light,
turning on the light.
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