4-18 4203780 First Edition
ELECTRICAL
4
Theory of Operation and
Sub-Circuit Schematics
Power 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
30-amp circuit breaker (F2) input terminal and from
circuit breaker (F2) input terminal to 10-amp circuit
breaker (F5).
Unswitched power is available from 30-amp circuit
breaker (F2) output terminal to the following:
• Fuel pull-in relay terminal 30
• Accessory relay terminal 30
Unswitched power is provided from 10-amp circuit
breaker (F5) to PTO switch terminal E and then from
terminal E to time delay relay +12V terminal.
Unswitched power is also available from the battery
positive terminal to the battery terminal of 50-amp circuit
breaker (F3). From circuit breaker (F3) unswitched power
is available to glow plug solenoid battery terminal and to
30-amp circuit breaker (F7). Circuit breaker (F3) also
provides protection to the alternator 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.
Switched Power Circuit
When the key switch is turned to the run position, voltage
is provided from key switch terminal I to accessory relay
terminal 86, energizing the relay. With the relay
energized, switched power is provided from accessory
relay terminal 87 to the following components:
• Alternator terminal I
• Fuel shutoff solenoid hold-in coil
• PTO switch terminal B
• Seat switch
• 10-amp circuit breaker (F4)
• 10-amp circuit breaker (F6)
Switched power is provided from 10-amp circuit breaker
(F6) to the following:
• 4WD switch
• Diff lock switch
• Fuel pump
• Horn relay terminals 30 and 86
• Brake pedal switch
• Cab/Canopy option connector (J4) terminal 4
With switched power provided to the fuel pump, the fuel
pump starts to operate.
Switched power is also provided from 10-amp circuit
breaker (F4) to the following:
• Volt meter
• Engine temperature gauge
• Tachometer
• Hour meter
• Fuel gauge
• Air filter service light
• Return filter service light
• Hyd oil temp light
• Charge filter service light
• Low charge pressure light
• Engine coolant temp light
• Engine oil pressure light
With switched power provided to the gauges and hour
meter, the gauges start to operate and the hour meter
starts logging hours.
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