I would not cut the wire. Thi is just simply a rubber grommet that goes through the tailgate. On the inside of the tailgate, remove the black cover and the bracket for the wiring. You can also pull the pins/contacts at the end of the wiring to pull it through the hole in the tailgate. Then find a solid rubber grommet to put back in the hole. Lowe's normally carries them. IMHO if you cut the wire you are opening yourself up for a short and blown brake light fuses.
My 99 had a grommet on the inside of the tailgate that fit the wiring hole on the outside of the tailgate perfectly.
" ... Nobody said it was a good plan. It's like somebody went through an actual strategy and replaced every instance of the word 'tactical' with 'balls out.' ... "