I had to replace a bulb a few years ago, sorry all I can remember is it is a H3 bulb. It may well be a 55W. Before you go chasing an intermittent electrical problem just replace the bulb. It is possible that the filament is broken but does not have a piece missing so that when you hit a bump the ends touch and they provide enough of a contact to "weld" itself back together enough to work. When changing the bulb remove and replace the one you are taking out several times, it will help clean up the contacts on the plug, just in case you have built up some corrosion on it.
bob