DIMMER SWITCHESThe headlight switch

DIMMER SWITCHES
The headlight switch controls the power or hot side of the headlight
circuit. The current is then sent to the dimmer switch, which allows
current to flow to either the high-beam or the low-beam filament of
the headlight bulb, as shown in b FIGURE 56 28.
An indicator light illuminates on the dash when the high beams
are selected.
The dimmer switch is usually hand operated by a lever on the
steering column. Some steering column switches are actually attached
to the outside of the steering column and are spring loaded.
To replace these types of dimmer switches, the steering column
needs to be lowered slightly to gain access to the switch itself.
AUTOMATIC DIMMING
MIRRORS
PARTS AND OPERATION Automatic dimming mirrors use
electrochromic technology to dim the mirror in proportion to the
amount of headlight glare from other vehicles at the rear. The electrochromic
technology developed by Gentex Corporation uses a
gel that changes with light between two pieces of glass. One piece
of glass acts as a reflector and the other has a transparent (clear)
electrically conductive coating. The inside rearview mirror also has
FIGURE 56 27 Typical daytime running light (DRL) circuit. Follow the arrows from the DRL module through both headlights. Notice that
the left and right headlights are connected in series, resulting in increased resistance, less current flow, and dimmer than normal lighting.
When the normal headlights are turned on, both headlights receive full battery voltage, with the left headlight grounding through the DRL
module.
a forward-facing light sensor that is used to detect darkness and
signal the rearward-facing sensor to begin to check for excessive
glare from headlights behind the vehicle. The rearward-facing sensor
sends a voltage to the electrochromic gel in the mirror that is
in proportion to the amount of glare detected. The mirror dims in
proportion to the glare and then becomes like a standard rearview
mirror when the glare is no longer detected. If automatic dimming
mirrors are used on the exterior, the sensors in the interior mirror and
electronics are used to control both the interior and exterior mirrors.
b SEE FIGURE 56 30.
FIGURE 56 28 Most vehicles use positive switching of the
high- and low-beam headlights. Notice that both filaments share
the same ground connection. Some vehicles use negative switching
and place the dimmer switch between the filaments and the
ground.
FIGURE 56 30 An automatic dimming mirror compares the
amount of light toward the front of the vehicle to the rear of the
vehicle and allies a voltage to cause the gel to darken the mirror.
FIGURE 56 29 A typical courtesy light doorjamb switch. Newer
vehicles use the door switch as an input to the vehicle computer
and the computer turns the interior lights on or off. By placing the
lights under the control of the computer, the vehicle engineers
have the opportunity to delay the lights after the door is closed
and to shut them off after a period of time to avoid draining the
battery.