I ran into an interesting time when it came to replace the taillight 
bulbs in the van a while back.  The bulbs are 5 watt, but nobody 
stocks the same bulb (other than the dealer!).  The bulbs in Europe 
are rated by wattage.  The bulbs here are rated by candle power (cp) 
or amperage depending what make they are.  Well, after many phone 
calls, and converting, nobody in North Anerica makes a 5 watt bulb to 
replace the taillight on the Vanagon.  An easy compromise, and 
cheaper one as well, was to change both bulbs to a GE89.  They 
are about 9 watts each.  The electrical circuit hasn't complained of 
the extra load, and they are brighter (safer) when in fog, rain, etc. 
BTW, the 5 watt German bulb was over $2 each, and I purchased
3 GE89 bulbs for $2.43 with tax.

If anyone wants to use the correct German bulbs, BMW dealers stock 
all of them.  The BMW's MUST use correct wattage bulbs so that the 
computer knows if there is a bulb burned out or not, and to turn on a 
dash light.  Apparently, the BMW's computer counts the load on a 
circuit and that's how a failed bulb is detected..