Pulse Width Modulation: Is frequently found in the electrical systems that run the headlight circuit in many modern vehicles, and when it comes to HID or LED upgrades, that's a problem since it results in constant flickering on the new setup Do you need these? Not sure whether or not you'll need these when doing an upgrade on your vehicle? Check out the rule of thumb guide in the tech specs below for some information to help you make the best decision. If you are unsure, GTR Lighting recommends installing the PWM Modules, since it wont harm anything even if un-needed. Anti-Flicker: With their powerful Capacitors system inside, these will absorb the pulsing current coming from your factory wiring and smooth it out before it causes your LED bulbs or HID ballasts to flicker. In most cases, they can be used alone, and in other cases, can be used in conjunction with a relay harness to ensure smooth, uninterrupted power delivery. Construction: GTR Lighting is known for producing the highest quality HID and LED accessories on the market, and these are no different. Their die-cast housings allow for the internals to be fully potted and protected against the elements. The integrated mounting point is a nice touch. The braided mesh insulation will protect the wiring forever, and the over-molded connections are as corrosion-resistant as it gets. Plug and Play: No need for complicated wiring to solve this common issue. The GTR Ultra 2.0 Anti-Flickers are easy to setup. With an input and output that is specifically sized to match your original wiring and the input of the bulb or ballast you're using these will simply plug n play in between. Daytime Running Lights: Often run off both pulsed voltage, and low voltage. It's important to understand which one your car uses - because if you're having issues with a low voltage setup, these will not solve that problem (since they don't increase the voltage coming from the car... they just smooth it out).