There are several bulbs within each of the gauges. They're all the same type. The bulbs within the idiot lights, are the same, as well. Best to replace all of them, at the same time: you have to disassemble the idiot light assembly anyway, you might as well do them all at the same time. Otherwise, you will likely be tearing it all apart in a few months again...
The gauges have some type of oil inside of them, so try to keep them face up, as much as possible, or the oil/liquid may run out -- don't ask me what it is, I just know the Clymer manual warns against it; I suspect it is a dampening fluid, of some sort, for the needles.
I would suggest you replace all of the light bulbs on the bike. There are
1156LL/
1157LL bulbs, which have a longer life (LL); 1156 is a single filament, turn signal light, while the 1157 is a dual filament, running/brake light bulb. That is what I put in my bike, the LL bulbs. By changing all of the lights, at the same time, you know you most likely won't have to worry about them for several years to come. It is a bit more work, but the security of knowing that they are all new, is worth it, in my mind. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII