definately run a relay, this way you can use a small micro switch without worrying about the amp rating. and it keeps the fuel pump power wire intact....yes you cut it, but the contacts of the relay basically is a wire, so it's like adding an inch and a half of wire to the middle of the power wire, so there is little that can fry on that side. The coil is a low current device so hook to power (acc) and the other side to the switch then to ground. A micro switch can be mounted almost anywhere, and if you get a thin push on push off, you can hide it under the carpet.