ELECTRICAL SYSTEM ATTACHMENTS
ELECTRICAL GAUGES AND
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.
Sending Unit for Water
SENDING UNIT FOR WATER TEMPERATURE
1. Connection. 2. Bushing. 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
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
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.
Sending Unit for Oil Pressure
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.
Electric Hour Meter
WIRING DIAGRAM FOR ELECTRIC HOUR METER
1. Electrical hour meter. 2. Pressure switch. 3. To
alternator or battery.
The electric hour meter (1) measures the clock
hours that the engine operates. The electric hour meter
(1) activates when the pressure switch (2) closes. The
pressure switch (2) closes the circuit from the positive
terminal on the alternator or battery when the engine oil
pressure is above approximately 6 psi (40 kPa).