Actually, very few of the original switches in the Xterra can handle 20 amps. That's why there are so many relays in the X. A 20 amp switch gets pretty big.

Another thing to watch out for is the inrush current of incandescent lamps. The inrush can fry a switch or relay that isn't rated for it. A good rule of thumb for incandescents is that the inrush current is 10 times the operating current.