Electrical System

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 contactor 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.

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. The chart shows components that operate together.

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.