How To: Test The Polarity Of V-LEDS

Posted: February 4, 2011 in How to:, Technical, Trouble Shooting
Tags: , , , ,

My last post was on how to make a quick and easy test light. This is a little trick you can use to test your LEDs. Use this to verify which contact on your LED is the positive and the negative. If you think you have a defective LED you can use this to confirm if it’s the LED that’s not working or if your cars socket is the problem. Items needed to make this tester include a fresh 9 Volt Battery, a couple of lengths of wire and some electrical tape. This is easy to do, lets cover the steps.

Look at the picture below. Start out with your wire, tape and battery. Strip some sheathing off of both ends of the wire. Fold back the wire on one end. Note the positive and negative terminal of the battery and place the wire on top of each terminal. Fold the tape over and use it to hold the wire onto the terminals of the battery. And you’re done!  To use this new tool just touch the bare wires from picture #4 to the contacts of the LED, note which wire is positive and negative. If the LED  lights up you have the polarity correct. If the LED does not light up, reverse the wires and try again. If it still doesn’t light up than either the battery is dead or the LED is not working.

This little battery tester has helped me in may different ways. If you do not have a 9 volt battery, any battery will do. I have done this with power tool batteries too, just don’t use any batteries larger than 12 volts. You can use this for more than just testing LED lights. I first used this setup to test for speakers in cars when the radio harness was cut off. After I located all of the power wires I would use this to test the remaining wires to match up the pairs of speaker wires. And you can see the speaker move in or out too, which tells you what speaker wires are positive and negative.

I have had people ask me if you can get shocked by touching both wires at the same time, the answer is no. It is very rare that you would get shocked by 12 volts DC power; it is possible, but you would have to be trying really hard.

Thanks for reading. If you have another use for this type of tester of if you have another invention that you use on a regular basis please share. You can email me direct at: or leave a comment below.

James, the

  1. Jackson says:

    Perhaps it might be a good idea to add a polarity mark on V-LED products? Maybe a black marking, or a corner cut out, much like polarity markings on LEDs. I know the connectors on cars typically won’t have polarity markings to match up with, but this may have things covered on V-LED products end for any application type.

    I realize the labor/value added costs involved in this probably wouldn’t justify the practicality, but just an idea =)

  2. You answered the question for me. Without testing the cars sockets for polarity the markings on the LED would not be that useful. On another note we have already started making dual polarity LEDs that work regardless of the polarity of the socket. We hope to bring this feature to all of our products in the future.