ELECTRICAL
673831-Rev A 4-17
4
Start Circuit—Theory of Operation
Unswitched Power Circuit (Red)
Unswitched power is available from the battery positive
terminal to the 3-way distribution block.
Unswitched power is available from the 3-way distribution
block to the following:
• Starter motor battery terminal
• Alternator battery terminal
• 40-amp fuse (F2)
• 30-amp fuse (F3)
• 15-amp fuse (F4)
• 30-amp fuse (F5)
• 20-amp (F6)
• 20-amp fuse (F7)
• 30 amp fuse (F9)
Unswitched power is available from 40-amp fuse (F2)
output terminal to the glow plug relay (K2) terminal 30.
Unswitched power is available from 30-amp fuse (F3)
output terminal to the ignition relay (K1) terminal 30.
Unswitched power is available from 15-amp fuse (F4)
output terminal to the following components:
• Ignition switch terminal 6
• LDU Display terminal 1-01
Unswitched power is available from 30-amp fuse (F5)
output terminal to the fan motor (M4) terminal 1.
Unswitched power is available from 20-amp fuse (F6)
output terminal to the MCU (U1) terminals 6-06 and 6-07.
Unswitched power is available from 20-amp fuse (F7)
output terminal to the MCU (U1) terminals 1-01 and 1-01.
Unswitched power is available from 30-amp fuse (F9)
output terminal to the starter relay (K3) terminal 30.
Interlock Circuit
The interlock circuit sets the mower in a condition that will
allow the engine to start. The interlock conditions are:
• Mow switch (SW2) in the off position, no voltage
detected at MCU (U1) terminal 4-09
• Parking brake switch (SW5) in the on position,
switched power detected at MCU (U1) terminal 4-08
• Traction pedal is in the Neutral position, neutral
switch is closed and switched power is detected at
MCU (U1) terminal 4-10
With the mow switch in the off position, the parking brake
switch in the on position and traction pedal in the Neutral
position, power is sent from MCU terminal 2-06 to the
fuel solenoid (SOL12) hold-in coil terminal H and the
engine can start when the keyswitch is turned to the Start
position.
Glow Plug Circuit
When the key switch is turned to the run position, voltage
is sent from key switch terminal 2 to MCU (U1) terminal
4-07.
The MCU sends switched power from terminal 5-08 to
the glow plug relay (K2) terminal 30, energizing the relay.
With the glow plug relay energized, voltage is provided to
the glow plug terminal, heating the glow plugs. The glow
plug icon will be shown on the display. Glow plug timer is
determined by the temperature sender input:
• Below 55° F (13° C) - 8 second timer
• 55° - 91° F (13° - 33° C) - 5 second timer
• 91° - 120° (33° - 49° C) - 3 second timer
• Above 120° F (49° C) - 0.5 second timer
Starter Circuit
When the key switch is turned to the start position, the
interlocks are set and the glow plug timer ends, voltage is
provided from MCU terminal 1-06 to start relay (K3)
terminal 86, energizing the relay. With the relay energized
voltage is provided to starter motor solenoid terminal S,
energizing the solenoid. With the starter solenoid
energized, voltage is provided from the starter solenoid
contacts to the starter motor, engaging the motor.
Fuel Solenoid Circuit
With the starter motor solenoid energized, voltage is
provided from starter motor terminal F to the fuel
solenoid (SOL12) pull-in coil terminal H, energizing the
coil. With the pull-in coil energized, the solenoid plunger
retracts. When the solenoid plunger is fully retracted, an
internal switch opens the pull-in coil circuit. This prevents
extended activation of the high-current pull-in coil. The
hold-in coil keeps the solenoid plunger in the retracted
position until it is de-energized. With the solenoid plunger
retracted, fuel is allowed to flow, and as the starter motor
cranks the engine, the engine starts operating.
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