How to wire LED lights to 12-Volt car wiring

Written by cassandra tribe
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How to wire LED lights to 12-Volt car wiring
The longer lead is the anode and the shorter is the cathode. (red led image by Kir from

LEDs are bright, low-powered lights that are used to add custom styling to vehicles and as power indicators for a variety of switches and functions. Requiring only 2 volts of power, a resistor must be included in the path of the circuit wire for LED lights to a 12-volt auto wiring system. Without the resistor, the LED will blow out. Each LED must have its own resistor to protect the circuit. Single LED lights typically come with a simple, round holder that uses pressure from screw nuts to secure the light into place on the dash, making them easy to mount into place.

Skill level:

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Things you need

  • spanner
  • Drill (if needed)
  • Mounting hardware
  • Screwdriver
  • LED light
  • Resistor
  • 14-gauge electrical wire
  • Electrical pliers
  • Soldering gun
  • Solder
  • Wire brush
  • Plastic zip ties
  • Switch (if desired)

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  1. 1

    Open the bonnet of the car and disconnect the negative cable from the battery by loosening the locknut on the terminal with a spanner and pulling the cable off.

  2. 2

    Decide where the lights will be placed in the vehicle. Drill and mount any necessary hardware included with the lighting kit or use pre-existing slots or holes in the car to mount the LED light.

  3. 3

    Pass two wires through the hole where the LED will be mounted. This will allow the connection to be made before the light is secured into place, making it easier to work on.

  4. 4

    Pull one of the wires through the firewall (where the car electric harness passes through) and up to the positive post on the battery (this will be the LED power wire). Wrap the end around the positive post so that the wire does not get pulled back into the car.

  5. 5

    Pull the other wire along the same path through the firewall and wrap it around something close to, but not touching, the negative terminal of the battery. This will be the ground wire of the LED.

  6. 6

    Strip the insulation off both ends of the wire that runs to the positive terminal of the battery with electrical pliers.

  7. 7

    Solder one end of the wire to the positive terminal on the battery and the other to the longer lead on the LED. Know that LEDs have two leads; one is noticeably longer than the other.

  8. 8

    Strip the insulation off both ends of the wire that runs to the negative terminal of the battery (ground wire) with electrical pliers.

  9. 9

    Solder one end of the ground wire to the shorter lead on the LED. Do not attach the wire to the battery terminal.

  10. 10

    Cut the ground wire 40 cm (16 inches) away from the negative post of the battery and strip the insulation off of the two ends of the wire.

  11. 11

    Solder one end of the ground wire to each end of the resistor. The resistor does not have a direction; either end can go with either wire.

  12. 12

    Solder the remaining end of the ground wire to the negative terminal on the battery.

  13. 13

    Push the LED light into position and attach the mounting hardware according to the instructions included with the kit.

  14. 14

    Use zip ties to hold the LED wires up and out of the way by attaching them to the underside of the dash or bundling the wires with the electrical harness.

Tips and warnings

  • To connect an LED to a pre-existing switch, run the power wire to the power side of the switch and not the battery. Move the wire from the resistor to the negative terminal of the battery to a good grounding point on the car's frame. This way, the LED will light only when the switch is engaged.
  • Use a resistor that matches the ratings listed on the LED package or the bulb can blow out from being overwhelmed by voltage.

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