Sometimes when installing a new LED bulb replacement you'll find that the bulb won’t illuminate. Not to worry! Simply take the bulb out, rotate it, and put it back in the opposite way. LED bulbs have two sides (polarity specific) and only illuminate when installed correctly. Here's why:
LEDs, which stand for Light Emitting Diodes, are very similar to standard Diodes. A Diode allows current to flow in only a single direction and is made from an anode and cathode. The current will flow inside the Diode from the positive anode to the negative cathode.
So much like the standard Diode, the Light Emitting Diode, an LED, also has a positive and negative side. If your LED bulb doesn’t illuminate the first time just give it a flip!
The same concept applies to HID kits as well, polarity will play a role when installing your HID bulb kit into your vehicle. The best and most efficient way to ensure your kit is properly installed is to test as you go through the install process. If you install your Relay harness, ballasts, and bulbs, yet they do not power up or just one side will not power up, start unplugging and rotating connectors 180° around and plugging them in again. If the pins in the connections do not line up in terms of their proper polarity (negative, positive), the circuit cannot be complete and will not power on your HID kit. Once you have all the connections sorted and polarity is restored, the kit will function properly!
Here you will find a video referring to reverse polarity and shows a visual demonstration of how to troubleshoot Reverse Polarity.