[petek]

You can test each lead to the battery without blowing up the lamp (assuming a #6104 bulb is an incandensant (i.e. normal) bulb).

If you have a good ohm meter you and determine which lead is which by ohm'ing everything out. Greatest resistance is between the high and low beam leads. Lowest resistance is between the high beam and common. "Medium" resistance between the low beam and common.