Principles Of Operation; Safety Interlock System - Simplicity Legacy Series Service & Repair Manual

• OFF grounds the engine ignition coil through the igni-
tion switch, preventing ignition system sparking. The
safety interlock system creates its own "OFF" circuit if
an unsafe situation exists. The safety system
grounds the ignition coil using a combination of:
1) the PTO switch and seat switch
or
2) the brake pedal switch and seat switch
if an operator is not present in the seat.

Principles of Operation

IGNITION SHUTDOWN SYSTEM
When the ignition switch is in the "START" or "RUN" posi-
tion, the ignition circuit is open, allowing the engine to
run.
When the ignition switch is turned to "OFF," the engine is
shut off by the following:
Air-Cooled Engines
The ignition switch closes, which grounds the ignition
coil.
Liquid-Cooled Engines
The ignition switch opens, which shuts off power to the
ignition coil.
Diesel Engines
The ignition switch opens, which shuts off power to the
fuel pump and solenoid.
CHARGING SYSTEM
While the engine is running, current flows from the alter-
nator to the positive battery post and charges the battery.
CRANKING SYSTEM
The cranking system is composed of the ignition switch,
the safety interlock switches, the PTO switch, the
solenoid, and the starter.
Cranking system current path:
1. Current travels from the battery through the circuit
breaker, through the ignition switch, through the safety
switches to the solenoid.
2. If all safety conditions are met, the safety interlock
switches allow current to pass through the solenoid,
activating the solenoid. The activated solenoid sends
power to the starter, cranking the engine.
7 Electrical System Service

Safety Interlock System

The safety system can be divided into two sub-systems:
1. the Operator Present sub-system and
2. the Safety Starting sub-system.
Operator Present Sub-System
The operator present sub-system is designed to protect
the operator from injury if the operator would leave the
seat.
1. Engine should shut off when the operator rises
off the seat if ANY of the following conditions
exist:
A. Brake pedal is not depressed.
B. PTO clutch switch is engaged.
C. Cruise control lever is engaged.
2. Engine should remain on when the operator rises
off the seat ONLY if ALL of the following condi-
tions are met:
A. Brake pedal is fully depressed (or parking brake
set).
B. Electric clutch switch disengaged.
C. Cruise control lever is not engaged.
Safety Starting Sub-System
The safety starting sub-system will prevent the engine
from cranking if any of the following conditions exist.
1. Engine should NOT crank if ANY of the following
conditions exist:
A. PTO clutch switch is engaged.
B. Brake pedal is not depressed.
C. Cruise control lever is engaged.
2. Engine should crank ONLY if ALL of the following
conditions are met:
A. Electric clutch switch disengaged.
B. Brake pedal is fully depressed (or parking
brake set).
C. Cruise control lever is not engaged.
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General Information