I found this interesting yesterday when I decided to change the regular 3157 bulbs in the 01 L tails to superwhite (duller by the way stick w/ stock bulb), I tried just for giggles to change the reverse light bulb with the same one and it worked, a 3156 replaced by a 3157. Anyone else tried and noticed this for this bulb, or any others for that matter?

 

The 3157 is a dual filliment bulb, where the 3156 is a single. However the brighter filliment on the 3157 is the same as the 3156 and is wired the same.(wires are located the same place on the base) The lower wattage filliment on the 3157 is wired closer to the insind of the terminal. You can use a 3157 in the place of a 3156 but not a 3156 in place of a 3157.