Not all of the wiring is 14 gauge and you would not get the benefit of color coded wiring. Spools of stranded copper wire are really expensive right now and it may just be cheaper to buy the kit.
I replaced most of the wiring on my truck (not all the same time), with off the shelf black and red wire, several boxes of crimp connections and several trips to FLAPS ended up spending more than a harness would have cost. Although my wiring is now good, I don’t have the benefit of color coding.
If it was me, I would bite the bullet and buy a kit, its straight forward and quicker, as you would not have to make every crimp/solder joint and you’ll have instructions on how to do it.
