ELECTRICAL SYSTEM ATTACHMENTS SYSTEMS OPERATION 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. GAUGE 12V 24V 32V WATER TEMPERATURE Sender 5L7443 5L7442 5L7442 Gauge 5L7446 5L7444 5L7444 Resistor 5L7441 OIL PRESSURE Sender 5L7450 5L7450 5L7450 Gauge 5L7455 5L7456 5L7456 Resistor 5L7441 Sending Unit for Water Temperature 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 (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. 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). 11