You want to cut the OD wire. I recommend cutting it withing a few inches of the connector on the rear of the shifter frame. If you haven't already done so, you have to remove the center console to see the connector. Only cut the wires and save the sleeve for use with the new shifter's wires. Also, before you do anything, make sure the new shifter handle's wires are long enough. If you cut the wires inside the shifter handle instead of near the connector, you'll probably have to do a solder splice instead of a crimp splice because of the tight space. Also, you will want to loosen the shifter frame to allow you to unclip the wires as they pass under the frame. One of the four bolts is under the shift rod. You don't have to remove that bolt completely. Just use an open ended wrench to loosen it.
Here's a tip to make the installation job easier. When you turn off the car, keep the brake pedal pressed. This releases the shifter lock so that you can check the operation of the new shifter handle without turning on the car to get it out of park. (Note: This worked for me while I was working on the shifter, but didn't work when I tested it a week later. ???)
In case you need this, the center console is held in by a screw in the rear cup holder and two push clips in the front. If you have a Zeta armrest, you have to remove it first.