Electrical System

Wiring Diagram Notes

Only one fuel shutoff solenoid will be installed on the engine. Only the wires for the installed solenoid will be provided.

Wiring Diagram

Components

Water Temperature Contactor

A water temperature contactor switch is located in the cooling system. This unit is non-adjustable. Thermal expansion of the element operates a micro-switch that can be used to signal an operator or control a device. The water temperature element must be in contact with the coolant. After an overheated engine is allowed to cool, the water temperature contactor switch automatically resets itself.

Oil Pressure Switch

An oil pressure switch is located in the oil system. This switch has three terminals and can serve a dual purpose. This switch senses the oil pressure. When the oil pressure falls below a preset pressure the switch deactivates. When the pressure rises again beyond a preset pressure the switch reactivates. This switch can be used to signal an operator that the engine oil pressure has dropped.

Control Relay

This is a standard type relay that, when energized, has contacts that open across one circuit and close across another circuit. The circuits are wired so that when the relay is energized voltage from the battery will go to and energize the fuel shutoff solenoid (on engines equipped with an energize to run type of solenoid). On engines which use a latching type (energize to shutoff) fuel solenoid, the control relay is de energized and voltage flows from the battery to the STOP terminal on the fuel shutoff solenoid. This in turn shuts down the engine.

Electrical Gauges and Sending Units

The electrical gauges and sending units operate in electrical balance. Because of this, the voltage and resistance ratings are important to get the correct indications on the gauges.

Water Temperature Sending Unit

Sending Unit for Water Temperature
(1) Connection. (2) Nut. (3) Bulb.

The sending unit for water temperature is an electrical resistance. It changes the value of its resistance according to the temperature which the bulb (3) feels.

The sending unit is in a series circuit with the electrical gauge. When the temperature is high, the resistance is high. This makes the gauge have a high reading.

The sending unit must be in contact with the coolant. If the coolant level is too low because of a sudden loss of coolant while the engine is running or because the level is too low before starting the engine, the sending unit will not work correctly.

Oil Pressure Sending Unit

Sending Unit for Oil Pressure
(1) Connection. (2) Fitting.

The sending unit for oil pressure is an electrical resistance. It has a material which changes electrical resistance according to pressure which it feels.

The sending unit for oil pressure is in a series circuit with the electrical gauge. As the pressure on the sending unit changes, the reading on the gauge changes in the same way.

Magnetic Pickup

Schematic of Magnetic Pickup

The magnetic pickup is a single pole, permanent magnet generator made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of force around the pickup, an AC voltage is made. The ratio between the frequency at this voltage and the speed of the engine is directly proportional.

Rear Power Takeoff Clutch

Power Takeoff Clutch (Typical Illustration)
(1) Ring. (2) Driven discs. (3) Link assemblies. (4) Lever. (5) Key. (6) Collar assembly. (7) Nut. (8) Yoke assembly. (9) Hub. (10) Plates. (11) Output shaft.

Power takeoff clutches (PTO's) are used to send power from the engine to accessory components. For example, a PTO can be used to drive an air compressor or a pump.

The PTO is driven by a ring (1) that has spline teeth around the inside diameter. The ring can be connected to the front or rear of the engine crankshaft by an adapter.

NOTE: On some PTO's located at the rear of the engine, ring (1) is a part of the flywheel.

The spline teeth on the ring engage with the spline teeth on the outside diameter of driven discs (2). When lever (4) is moved to the ENGAGED position, yoke assembly (8) moves collar assembly (6) in the direction of the engine. The collar assembly is connected to four link assemblies (3). The action of the link assemblies will hold the faces of driven discs (2), drive plates (10) and hub (9) tight together.

Friction between these faces permits the flow of torque from ring (1), through driven discs (2), to plates (10) and hub (9). Spline teeth on the inside diameter of the plates drive the hub. The hub is held in position on the output shaft (11) by a taper, nut (7) and key (5).

NOTE: A PTO can have from one to three driven discs (2) with a respective number of plates.

When lever (4) is moved to the NOT ENGAGED position, yoke assembly (8) moves collar assembly (6) to the left. The movement of the collar assembly will release link assemblies (3). With the link assemblies released there will not be enough friction between the faces of the clutch assembly to permit a flow of torque.