Headlight Circuit

Headlight Circuit

[Diagram]

This circuit is a very good example that contains all of what we have learned so far in Electrical Automotive.  This diagram shows the circuit of how headlights are generally wired up.  The circuit contains resistors (light bulbs), fuses, a relay and various circuit diagram symbols like grounding and resistors.

Components:

·         Battery (power supply)

·         Wire

·         Fuse

·         Relays x2

·         Light bulbs x2

·         Switch

Function:

The battery supplies power at the Power Distribution Point.  Wire carries the positive to the relays  at terminals 30.  The relays are used as a remote switch, main purpose is so that high voltage wire does not need to pass through the switches that are used by hand. Relays work by a magnetic coil that is powered with a small amount of voltage, which is then operated by a switch (operated by hand).  When this switch closes the circuit, a small amount of voltage powers the coil inside the relay, and attracts the switch inside to close, letting current of higher voltage to pass through terminals 87 (or 87a) and 30. 86 is the terminal where the relay is fed power, at this end a switch is mounted in to open and close the circuit.  85 is where the relay is grounded. (negative)

As we can see, the light bulb has three points, the centre one being ground, the left point being low beam and the right point high beam.  When low beam is switched on,  only one point of the bulb to the centre point will glow, and when high beam is on, both  ends will glow.  that end could also have higher resistance to glow brighter.