TM 9-2320-269-20-1
ELECTRICAL SYSTEM - GAGE AND SENDING UNIT SYSTEM
GENERAL
The gage and sending unit system measures and indicates the working condition of the vehicle using electrically and
mechanically operated components. The system consists of an ampere gage, engine oil pressure gage and sending unit,
engine oil pressure lockout switch, engine water temperature gage and sending unit, transmission oil pressure lockout
switch, hourmeter, fuel level gage and sending unit, speedometer and drive adapter, two tachometers and a drive adapter,
and two air pressure gages, and an air pressure switch.
AMPERE GAGE
The ampere gage is an electrically operated gage mounted in the left side of the instrument cluster panel. It indicates
battery charge and alternator output.
ENGINE OIL PRESSURE GAGE AND SENDING UNIT
The oil pressure gage is an electrically operated gage mounted in the left side of the instrument cluster panel that indicates
the engine oil pressure when operating. It receives an electrical signal from a pressure sensitive sending unit mounted in
the oil cooler.
ENGINE OIL PRESSURE LOCKOUT SWITCH
The oil pressure lockout switch is a pressure-sensitive switch mounted in the oil cooler. It shuts the engine off by opening
the electrical circuit to the in-tank fuel pump if the engine looses oil pressure. TRANSMISSION OIL PRESSURE
SENDING UNIT
The oil pressure sending unit is a pressure-sensitive switch mounted in the side of the transmission. It shuts the engine off
by opening the electrical circuit to the in-tank fuel pump if the transmission gets too hot.
HOURMETER
The hourmeter is an electrically operated gage mounted below the right side of the instrument panel that indicates the
number of hours the key switch is on.
SPEEDOMETER AND DRIVE UNIT
The speedometer Is a mechanically operated gage mounted in the right center of the instrument cluster panel that
indicates the vehicle speed in miles per hour. It is cable driven by a drive unit mounted in the transmission. The
speedometer contains an odometer that shows the accumulated mileage of the vehicle.
TACHOMETERS AND ADAPTER
There are two tachometers on the vehicle that indicate engine speed in revolutions per minute. One is mechanically
operated and mounted in the left center of the instrument cluster panel and is driven by two cables and an adapter unit
driven by the engine camshaft. The other tachometer is an electrically operated gage mounted on top of the derrick
operator's console that receives an electrical signal from the adapter unit in the drive cables.
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