Beechcraft C23 SUNDOWNER 180 Pilot Operating Handbook page 163

BEECHCRAFT
Sundowner
180 Section VII
C23 (M-1285
and
After)
.
Systems
Description
If installed, it is located
on the
right
side of the
fuselage (M-
1285
through M-2354)
or on the
left
side of the
fuselage
(M-2355 and
after)
aft
of the
wing. Airplanes equipped
with a
14-volt
electrical
system
require
a power
unit set to
13.75
to
14.25 volts,
while
those equipped
with
a
28-volt
electrical
system
require a
setting of
27.75
to
28.25
volts.
CAUTION
On
14-volt
airplanes,
the
power pin
for
external
power is
connected directly
tothe
bat-
tery
and
continually energized. Turn off battery
and alternator
switches
and all
electrical
and
avionics
switches
when
connecting the
auxiliary
power unit
plug.
Assure
correct
polarity (negative
ground) before connecting
auxiliary
power
unit.
Turn on the battery
switch before turning on the auxiliary
power
unit.
On
28-volt
airplanes, a reverse polarity
diode
protection
system
is
between
the external
power receptacle and
the
main
bus. With
external
power applied,
the bus
is powered.
Turn on the battery switch only,
with
all other
switches
including avionics
switches off,
when
connecting
the
auxiliary
power
unit. Assure
correct
polarity
before
connecting
external
power.
January,
1982
7-27