Electrical System Model (350 PAWN). The electrical system differences between the 350 PAWN and other
models are three additional panel lights, cold start switch, cold start solenoid and a different fuel shutoff solenoid.
1-5.2 illustrates the electrical system and figure 1-5.1 illustrates the electrical cold start system used on the 350 PAWN.
The 350 PAWN electrical system operates as follows:
When the emergency start switch (S1) is energized (pulled out), power is transferred through its contacts 1/4 and
applied to the upper contact of S2, and to contact 1 of S3 through the closed contacts of S4.
When the operator presses both the start switch S2 and the oil pressure bypass switch S3 (normal start sequence),
power is applied to contact 6 of K1 where it stops, and to the coil of K2 through the closed contacts of S4 and S3.
This causes relay K2 to become energized, its contacts 4/6 and 3/5 to close and power to be applied to the hold-in
coil of solenoid L1, and to the coil of relay K1, But because the hold-in coil of L1 is not sufficiently powerful to energize
L1, L1 stays de-energized until it receives power on its pull-in coil as described below.
When voltage is applied to the coil of relay K1, K1 becomes energized(normally open contacts 6 and 8 closes) and
voltage is applied to the coil of starter relay K3. Starter relay K3 then becomes energized which closes the S/M
Voltage is applied to the starter motor B1(energizing the starter for cranking the engine), to the pull-in coil of
L1 (energizing L1 which starts fuel flowing to the engine) and to the cold start solenoid through the cold start switch
S6 (normally closed below 40 °F) the starter fluid is injected into the engine.
When engine has started and start switch (S2) is released (Oil pressure bypass switch S3 only releases after pressure
is above 4 psi) voltage is terminated at the starter motor B1, pull-in coil of L1 and cold start solenoid.
When oil pressure is up and oil pressure switch S5 is subsequently released, an alternate path through S5 is provided
to keep K2 energized and the engine running.
Stop Circuits. The engine is stopped by pushing in the emergency stop switch (S1). The following
occurs when pushing the emergency stop switch:
Voltage to K2 through S1, S4, S5 and contacts 1/3 of K1 (while engine is operating) is terminated and K2 becomes
Voltage to the hold-in relay of L1 is terminated at contacts 6/4 and 5/3 of K2.
L1 closes the fuel shutoff valve and stops fuel flowing to the engine which results in shutdown of the engine.
K2 will become de-energized and engine shutdown in the same manner if either S4 or S5 open. S4 will open if the
V-belt breaks and S5 will open if oil pressure goes below 4 psi.
Light Circuits. The light circuit consist of a rheostat (R2) and four panel lights(DS1, DS2. DS3 and DS4).
When both S1 and R2 are on, current flows through each of the panel light which are connected to the rheostat in parallel.
Turning the knob on the rheostat controlls the illumination intensity (brightness) of the panel lights.
Charging Circuit. When the engine is running the alternator(G1) turns and produces approximately 14V
dc output. The 14V dc from the alternator (G1) provides 12 V dc to keep the relays engerized and recharges the
batteries (BT1 and BT2). Output voltage from the alternator is indicated on the ammeter by the needle pointing towards
discharge (minus) or charging (plus). Initially, at startup the needle on the ammeter will indicated a discharge. When the
engine is running correctly and the alternator operating properly the needle on the ammeter will indicate the batteries are