No you don't need to cut any wires close to the fuse box. You know where the "brain" of the alarm is? It's located right under the dash. It's a small device that has all the wires connected into. Now look for a solid yellow wire. That's your continous (+) wire. Now you have to remember to use a long enough wire that will reach from that yellow cable to where ever spot you want the push button and out to where the siren is. I'd give about a good 10 ft.
So tap the new wire to the (+) yellow wire, and then connect it to the switch. Using the output part of the switch, run the wire thru the firewall and connect it to the red (+) wire of the siren.
You're all done! Have fun whistling at those hunnies!