ELECTRICAL
4252490-Rev A 4-33
4
Instrumentation Circuit—Theory of
Operation
Power Circuit
When the key switch is turned to the run position, voltage
is provided from key switch terminal B to control module
terminals J1-2, J2-11, and J2-12, powering up the control
module. (See “Power Circuit—Theory of Operation” on
page 4-14.)
Hour Meter
When the key switch is turned to the start position,
voltage is provided from key switch terminal C to the
control module start input terminal J1-6, activating the
input. With the start input activated, the control module
engine run output terminal provides voltage to the hour
meter, and the hour meter starts logging hours.
With the hour meter connected to the control module
engine run output terminal, the hour meter only records
hours when the engine is operating.
Hydraulic Filter Pressure Light
When the hydraulic filter pressure switch closes, a
ground is provided from the switch to the hydraulic filter
pressure light, turning on the light.
Engine Coolant Temp Light (Diesel)
The engine temperature sensor resistance changes in
relationship to the engine coolant temperature. As the
engine temperature sensor is heated, the resistance of
the sensor changes from a high resistance to a low
resistance. The control module engine temperature input
terminal J2-1 measures the resistance of the temperature
sensor.
When the engine coolant temperature reaches 221° F
(105° C), the control module will deactivate the mow
circuit and raises the cutting units. The control module
then turns on the alarm light and activates the horn
circuit; the horn chirps twice per second. The control
module activates the alarm light and horn circuit for a
period of 60 seconds.
Engine Oil Pressure Light
When the engine oil pressure is below 7 psi (0.483 bar),
the engine oil pressure switch contacts close. With the
switch contacts closed, a ground is provided to the
engine oil pressure light, turning on the light.
Horn Circuit
When the horn switch is in the on position, voltage is
provided from the switch to the horn, activating the horn.
When the horn is activated by the control module, voltage
is provided from terminal J2-10 of the control module to
the horn.
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