Figure 4-47.-Typical stoplight switches.
Never bypass a fuse or circuit breaker by using
tinfoil or direct wire method. Always use the
correct amperage rating when replacing any
When this type of circuit is used, the front
indicator lamps and front signal lights must be
on a separate signal switch circuit.
To troubleshoot this type of switch, first find the
multiwire connector joining the main wiring harness to
the signal switch harness. Use a 12/24 volt test lamp and
the manufacturers maintenance manual as a guide. Test
the input and output of the switch. If the switch is at fault
and must be replaced, usually the steering wheel has to
be removed before the switch maybe removed.
Failure of the signal lights to flash is usually caused
by the flasher unit. A flasher unit is a nonrepairable item
mounted under the dashboard or on the fire wall.
fuse or circuit breaker.
Troubleshooting directional signals may be
somewhat complicated due to the fact that most of the
turn signal switches, flashing units, and much of the
wiring is located under the dashboard or in the steering
column. In addition, the most common design for a turn
signal system is to use the same rear lamps for both the
stoplights and the turn signals. This somewhat
complicates the design as the brake light circuit must
pass through the turn signal switch. As the left or right
turn signal is energized, the stoplight circuit for that
circuit is opened and the turn signal circuit for that
circuit is closed.
The two types of brake light switches are hydraulic
and mechanical (fig. 4-47). These may be mounted
under the dashboard, on the master cylinder, or on the
vehicle main frame. To test the switch, first check for
power to the switch. Then using a 12/24 volt test lamp,
touch the probe to the output terminal of the brake light
switch and apply the brakes. If the test lamp lights, the
switch is good. If the test lamp does not light, the switch
is defective and must be replaced.
The current draw of a horn is very high; therefore,
it is usually operated by a relay (fig. 4-48). The control
switch (horn button) is almost always mounted in the
Figure 4-48.-Typical horn circuit using a relay.