You must use a resistor from the 12v to the LED. If you hook up a 3 watt or less LED to the 12v it will burn out do to extra voltage. Unless you are very familiar with electronics, I would not attempt this, but wait until a product is available.
The only way you could hook up LED's without a resistor is to hook up enough LED's in a row so that the current draw is equivalent to 12v. Once you do this the only positive result is that the LED's will have a longer life than the standard bulb. They will now be using the same 12v draw as the bulb.
