[THEFERMANATOR]

Originally Posted by Destroyer

On the subject of Voltage. Remember that LED's are Light Emitting DIODES. They will only pass current in one direction. Think of it as a one way valve for electricity, much like a check valve works for hydraulics. They will not light if the current is flowing in the wrong direction. So if your brand new installation doesn't work, try reversing the positive and negative wires before you take it back to the store.
If anyone wants a really nice description of what a diode is and how it works read this: https://en.wikipedia.org/wiki/Diode

To add to this, if they don't light up, shut em off immidiately as feeding them backwards for to long can ruin them.