I have replaced my rear backup light bulbs with PIAA Xtreme white bulbs. They use the same wattage as the OEM but are brighter and whiter.
I could not find any bulbs with higher wattage. But I discovered if you bend one of the pins over, it will cause both filliments to light. All of the bulbs are 3157. They all have dual fillaments. but the backup lights only use one.
