11-89. ANNUNCIATOR PANEL.
11-90. DESCRIPTION. The annunciator panel is a small cluster of lights which warn of malfunctions in the
various circuits or systems. A malfunction is identified by the illumination of an individual warning light. There
are three amber warning lights and a push button test switch, (refer to Figure 10-1.) Power is supplied from the
bus bar through a 5 amp fuse located behind the instrument panel directly above the ammeter.
The VAC warning light is controlled by a vacuum sensor switch located at the firewall and is attached to the
vacuum regulator. The sensor switch will activate when the differential pressure is below 3.5 in. Hg.
The OIL warning light is controlled by an oil pressure sensor switch incorporated in the oil line to the oil
pressure gauge and is located at the firewall. The sensor switch will activate when the oil pressure is below 35
psi.
The ALT warning light is illuminated by current flowing from the bus bar to the alternator circuit, (refer to
appropriate alternator and starter schematic). This condition exists when the alternator is not operating properly
and the output is zero. During normal operation, the alternator warning circuit is also supplied with power from
the top diode terminal. This current flows through a 5 amp fuse, located aft of the diode heat sink, to the resistor
and diode creating a no-flow condition, which does not allow the warning light to light.
The test button is used to check the operation of the lights when the engine is running. The lights will work
when the engine is not running with the master switch turned on.
11-91. REMOVAL OF OIL PRESSURE SENSOR. Access to the sensor unit is gained by reaching up under the
instrument panel. Removal is accomplished by the following:
a. Disconnect the two electrical leads.
b. Unscrew the sensor unit from the bulkhead fitting.
c. Catch spillage and cover hole to prevent foreign matter from entering oil line.
11-92. INSTALLATION OF OIL PRESSURE SENSOR.
a. Seal sensor unit pipe threads with thread sealant tape (3M-Teflon 48 x 1/4).
b. Screw the sensor unit into the bulkhead fitting.
c. Reconnect the two electrical leads.
d. Perform operational check.
11-93. REMOVAL OF VACUUM SENSOR. Access to the sensor unit is gained by reaching up under the
instrument panel to the vacuum regulator. Removal is accomplished by the following:
a. Disconnect the two electrical leads.
b. Unscrew the sensor unit from the vacuum regulator.
c. Cover hole to prevent foreign matter from entering regulator.
11-94. INSTALLATION OF VACUUM SENSOR.
a. Screw sensor unit into vacuum regulator.
b. Reconnect the two electrical leads.
c. Perform operational check.
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY. 28, 1989
ELECTRICAL SYSTEM
2E5