I fitted a 21w bulb to my side light, it was a halogen one of the type that fit those tiny little indicators. Problem is, it blew. In fact it blew so hard that the top of the bulb flew off into the headlamp, where it remained until I managed to get it out with a bit of bent wire & a lot of patience. Lasted about 48hrs as I remember, I went back to a std side light bulb...