If you install your LED bulbs and they do not turn on you may have reverse polarity. What this means is the power and ground wires are your vehicles stock harness are reversed. What you will have to do is simply plug the LED bulb into the bulb socket backwards. This will not harm the vehicle or the kit.
Note: Reverse Polarity is an issue with the cars wiring not the LED bulb. Some cars come from the factory wired in an orientation that is reversed when compared to the LED bulb. When using stock halogen bulbs, polarity has no effect, therefore, some manufactures will have the power and ground wires opposite of the LED bulb. Some manufactures will have reverse polarity more then others. Most GM models have reverse polarity.