The shop manual says it is a 3W 12V. The parts list identifies it as Bulb, Wedge Base (12V/3W). The honda part number is 34908-MB0-003. If you have the old one you should be able to find something at the auto parts store by matching it up. If you don't. you probably need to go to the honda shop, but the bulb should not be too expensive
ATCnut
82 185s - sold
83 200x (hopped up)
84 200x (stock)
84 70 (lost this one to the DMV)
85 70 (soon to have lights, a foot brake, and CDI ignition)
84 200es (parts trike) - sold
85 350X (the best)
85 350X (siezed motor, dream of a poweroll kit someday)
85 250sx (frame was trash, got parted out)
86 250sx (the tractor)
86 250sx (a nicer tractor)
86 250sx (an even nicer tractor)
87 200x (parts trike, its really rough, a dog was chewing on it for a while)
87 250es Big Red (the tank!!)