Regarding using a PWM controller for LED's - this will usually work very well, but it must, I think, be use IN CONJUNCTION with a dropping resistor, not instead.  The reason is that the LED is in actuality a forward-biased diode and it has very low resistance.  Even a short-duration application of a high voltage will likely destroy the device.  As others have suggested you can put them in series to increase the voltage drop, but the bottom line is that the resistor or some other way to limit the current is required.  Then you can add the PWM circuit to dim the output from there.  If you are really talking about position lights there is no reason to dim them and hence you are back to a dropping resistor as the simplest, most reliable way to control the current.  It does waste energy, but I don't know of another (better) way.

Gary Casey