0003
TM 1-1740-221-13&P&P
THEORY OF OPERATION - (CONTINUED)
INDICATOR LIGHT, ENGINE OIL PRESSURE (PL6) Warning Light
Illuminates with a loss of engine oil pressure. This light is on until the engine is started. The normally closed oil
pressure switch supplies ground to the indicator light until engine has oil pressure. This engine oil pressure removes
the ground from the circuit which allows the light to go out or extinguish, as long as the engine has oil pressure.
INDICATOR LIGHT, ENGINE OVER-TEMP (PL7) Warning Light
Light illuminates if engine coolant temperature switch in the circuit closes. Temperature switch closes if coolant
temperature reaches 220 degrees.
ENGINE COOLANT TEMP GAUGE (G2) Indicates Engine Coolant Temperature
Temperature sending unit in the circuit allows current to low to the gauge proportional to the coolant temperature in
the engine.
FUEL GAUGE (G3) Indicates Amount of Fuel in the Tank
Fuel sending unit inside the fuel tank allows current to low to the gauge proportional to the level of fuel in the tank.
ENGINE OIL PRESSURE GAUGE (G4) Indicates Engine Oil Pressure
Oil Pressure sending unit in the circuit allows current to low to the gauge proportional to the amount of oil
pressure in the engine.
TRANSMISSION TEMP GAUGE (G5) Indicates Transmission Fluid Temperature
Transmission temp sending unit in the circuit allows current to low to the gauge proportional to the amount of
luid temp in the transmission.
VOLTMETER, BATTERY CHARGING (G6) Indicates Battery Charging Rate
Battery charging current is provided by the 90 amp alternator. The charging rate is determined by battery condition,
load and circuit condition.
INDICATOR LIGHT, BRAKE FAILURE (PL2) Warning Light
Light illuminates if the service brake system experiences a loss of brake pressure in any part of the system. If
the service brakes loose system pressure, pressure switch BFS located on top of the brake valve closes and
turns on PL2.
The following is a brief description of the various relays used to control various electrical circuits on the SATS
vehicle.
STARTER INTERLOCK RELAY (CRSI)
Energized with the hand brake lever engaged, which allows the engine starter relay to be energized as long as the
transmission shifter is in park.
HAND BRAKE RELAY (CRHB)
When energized (hand brake lever engaged), opens a set of contacts (FO-1, line 41) which prevents the
transmission from being engaged and closes a set of contacts (FO-1, line 40) which allows relays (CRI) and
(CRP) to be energized.
When de-energized (hand brake lever released), the hand brake relay contacts switch positions which allows
the transmission to be engaged.
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