How to convert a 12v bulb to a LED bulb

Written by david robinson
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How to convert a 12v bulb to a LED bulb
LEDs are replacing incandescent bulbs in many situations. (led image by sasha from

Light emitting diodes, or LED, bulbs are replacing small incandescent and neon bulbs in many electronic appliances. LEDs have many advantages over traditional bulbs. They last 100 times longer than tungsten bulbs, they don't shatter like glass bulbs, they use up to 90 per cent less electricity and they are non-toxic. The advent of 12-volt LEDs with bases designed to fit most 12-volt bulb-holders makes replacing 12-volt bulbs a realistic task for people with little or no electronic knowledge.

Skill level:

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Things you need

  • Digital multimeter

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  1. 1

    Switch on the power supply to locate the bulb and the wires supplying electricity to the bulb holder. Use a digital multimeter to establish which wire is positive and which is negative. Connect the positive and negative probes across the bulb holder. If the multimeter shows a positive reading, the positive probe is on the positive wire. A negative reading means the positive probe is attached to the negative wire. Mark or label the positive wire. Now switch off the power.

  2. 2

    Remove the bulb and place it somewhere safe. Check the polarity markings on the 12-volt LED. Insert the LED into the bulb-holder so the positive side of the LED connects with the positive side of the bulb holder. Push the LED firmly into the holder but do not use excessive force.

  3. 3

    Switch on the bulb. If you connected the LED correctly it will illuminate. If the LED does not illuminate, switch off the power, remove the LED, turn it through 180 degrees and reconnect it with the polarity reversed. Switch on the power and check again. If the LED still fails, try a different LED or put the bulb back in the holder to make sure the power is still working.

Tips and warnings

  • Buy one more LED than you need to allow for accidents, lost bulbs and circuit testing.
  • LED bulbs are small and easily mislaid. Keep them in a container when not in use.
  • Use 12-volt LEDS not standard 3.6-volt LEDS. Directly connecting a lower voltage LED to a 12-volt supply will destroy the LED.
  • If connecting LEDs to a vehicle, switch off the power by disconnecting the positive lead from the battery. This prevents accidental "short circuits" while handling circuit boards and moving wires out of your work space.

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