Blackout lighting control switches are designed to
prevent the service lighting from being turned on
accidentally. Their operation is described in the
"Headlight Switch" section of this TRAMAN.
Vehicles that operate on any public road must be
equipped with turn signals. These signals indicate a
left or right turn by providing a flashing light signal at
the rear and front of the vehicle.
The turn-signal switch is located on the steering
column (fig. 2-68). It is designed to shut off
automatically after the turn is completed by the action
of the canceling cam.
Figure 2-68.Typical turn-signal switch.
A wiring diagram for a typical turn-signal system
is shown in figure 2-69. A common design for a turn-
signal system is to use the same rear light for both the
stop and turn signals. This somewhat complicates the
design of the switch in that the stoplight circuit must
pass through the turn-signal switch. When the turn-
signal switch is turned off, it must pass stoplight
current to the rear lights. As a left or right turn signal is
selected, the stoplight circuit is open and the turn-
signal circuit is closed to the respective rear light.
The turn signal flasher unit (fig. 2-70) creates the
flashing of the turn signal lights. It consists basically of
a bimetallic (two dissimilar metals bonded together)
strip wrapped in a wire coil. The bimetallic strip serves
as one of the contact points.
When the turn signals are actuated, current flows
into the flasherfirst through the heating coil to the
bimetallic strip, then through the contact points, then
out of the flasher, where the circuit is completed
through the turn-signal light. This sequence of events
will repeat a few times a second, causing a steady
flashing of the turn signals.
BACKUP LIGHT SYSTEM
The backup light system provides visibility to the
rear of the vehicle at night and a warning to the
Figure 2-69.Typical turn-signal wiring diagram.