What Size Bulbs For Rear Number Plate Illumination?

[chrispy]

What size are the bulbs that illuminate the rear number plate (length and width preferably)? I was going to strip away the boot lining today to find out but it's hammering down with rain and I really don't want to get soaked. If anyone knows what size bulbs it takes (i'm assuming they're the festoon type as in the car's interior) for a 1997 C180 i'd be very greatful.

Thanks in advance to anyone kind enough to provide me with the info needed.

 

[Diesel Benz]

It should read in the car manual. From a US copy I can find: "C 5W"