Automotive wiring diagrams basic symbols

Automotive electrical diagrams provide symbols that represent circuit component functions. For example, a few basic symbols common to electrical schematics are shown as: (1) Switch, (2) Battery, (3) Resistor and (4) Ground.
Note that the switch symbol displays an open or closed circuit path, which is what an actual switch performs. The battery symbol appears to be made of layers or plates, common to internal battery construction.

The resistor symbol appears to impede energy flow, which is a resistor function. The case ground symbol indicates a connection pointing downward (ground) that dissipates energy.

Variations of symbols will exist depending on function or other characteristics. Examples are: Variable Battery symbol (5) and the Case Ground symbol (6).

Auto wiring diagram advanced symbols

 Abbreviated codes on the diagrams provide circuit path and part or component information. The codes or labels may be used to show circuit connector pin numbers, circuit values or component polarities that will add clarity to the diagnostic drawing. These sets of label examples are:
(1)A for Amperage or Amps. (2) ORN for wire diameter and color (3)1340 for Circuit Path ID (4)P for pass through grommet (5)A for Pin ID & Location (6)C1 for Terminal Connector ID (7)B+ for battery positive

automotive wiring electrical symbols

At first glance, a repair diagram may not convey how wires are of many colors and diameters (or gauges).
The diameter of each wire symbolized may be indicated by a label placed at some point along side its drawn line (1)(0.8).

Being aware of the color of a wire is important.(2) Wire color information is provided as a color code label in this case black/white.

(3)Also shown are common schematic illustrations of wires, (4)wires connected and (5) wires crossed but not connected.

For consistency in reading, most electrical schematics have signal or energy flow from top to bottom, with component inputs on the left and outputs on the right. With an understanding of how a system would function, the electrical diagram is probably one of the most valuable resources a technician can use in repairing a vehicle.

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AUTO / CAR WIRING DIAGRAM – BASIC CIRCUIT FOR INSTALLATION – RELAY CONNECTION – SPOT LIGHT / FOG LAMP INSTALLATION

When wiring anything in your vehicle that draws heavy current such as high powered offroad lights there are a few things to consider.  Number one, make sure you use wire that is rated for the amperage that the accessories is going to pull.  It is always better to have wire that is OVER rated rather than wire that is not rated high enough.  If wire is used that is not rated to handle the current that your accessory will pull, the result could be overheated wires that could melt the insulation, causing a short or worse yet it could result in a fire.  If you know how much current your accessory will draw you can determine what gauge wire is appropriate for your application.
 
   
Use wire that far exceeds the current draw of accessory.   It’s overkill but in a few applications we’ve used heavy gauge stranded industrial wire with water and chemical resistant insulation. That way there is no question as to whether the wire is rated high enough or not.  If this approach is taken, it is very wise to place a fuse at the battery end as close to the battery as possible.  Most wire in a vehicle, if shorted out, will burn up before the battery overheats and possibly explodes.  If wire that is over-rated for vehicle use is used and a short occurs, a short will most likely result in damage to the vehicle of some sort unless a fuse is put in line as close to the battery as possible.  With the fuse there, in the case of a dead short, the fuse will burn out first before any damage could occur.      
 
 With accessories that pull a lot of power it is always better to get your power directly from the batteries positive terminal rather than tapping into the existing fuse block or wiring harness.  In most cases the vehicles existing fuse block is not rated to handle the additional load of high powered accessories such as offroad / spot lights.  If you are the kind of person that likes to add all kind of goodies to your vehicle it might be worth installing an additional fuse block that handles non-critical items like offroad lights, CB radios, power inverters, etc.  This additional block can then be powered by a heavy duty wire capable of carrying the current required of all the accessories on the block.  Be sure to fuse the block at the battery.

In almost every case where high current is required the switch use to turn on the power should not handle the load.  That is better left to a relay.   What is a relay?  A relay is a device that, through a magnetic induction coil, turns on the power for you.  The switch that is installed in the cab of your 4×4 actually only powers the relay itself which draws very little current.  In most  installations a 30 AMP relay from Radio Shack (Auto Relay Cat. Number 275-226) will do unless your amperage demands exceed 30 amps.  Use a lighted or illuminated light switch in the cab to let us know if driving lights are on.
Offroad Lights or Accessory Wiring Diagram using a 4 – Pole Relay Relay

 
The method used for wiring the lights and other external accessories, for the most part, follows the diagram pictured above.  As in the diagram a wire is run from a 12 volt power source to the switch in the cab and out to the relay placing a fuse at the source of the power.  (Follow the relay’s wiring schematic when connecting the wires to the relay)  One of the relays terminals goes to ground.  Then run a heavy gauge wire from the battery to the relay placing a 30 Amp fuse in line very close to the battery.  Do not connect the power to the battery until all wiring is done.   Then I run a single heavy gauge wire out to the lights or other accessory. If installing lights, split it into two leads at the lights.  If you do this be sure the wire is rated to handle BOTH lights since it will carry the current of both.  The diagram shows two leads coming from the relay.  Then I run the second wire of the lights or other accessory to a good ground on the frame of the vehicle.  If the wires will not be soldered together and crimped connectors will be used it’s a good idea to put a dielectric paste on the connectors where they come in contact.  This will prevent corrosion as time passes ensuring a good connection.   Then double-checked all wiring before plugging in the power.  

  
Ohms Law

Ohm’s Law Defined

Ohm’s Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere.
( I ) Current is what flows on a wire or conductor. Current is measured in (A) amperes or amps.

( E ) Voltage is the difference in electrical potential between two points in a circuit. It’s the push or pressure behind current flow through a circuit, and is measured in (V) volts.

( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. The higher the resistance, the smaller the amount of current is allowed to flow. Resistance is measured in ohms.

( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts.

V = I x R
I = V / R
R = V / I 
  

Alternative Offroad Lights or spotlights or Accessory Wiring Diagram using a Relay