The correct bulb wattage is embossed on the taillight housing.
For replacements, use bulbs with the nickel-plated base (Osram, Philips, Sylvania). Stay away from the gold-anodized ones, as they show a different resistance to the circuit, which could potentially set off the dash indicator...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car