The factory wrapped harnesses with a tape that had no adhesive. Electrical tape leaves behind gunk when the vinyl unravels. Your wires are pretty clean so I do not think electrical tape was used, they would have old black goo on them.
This stuff works and this is not the only place to get it, just the easiest to find on a google search:
https://www.classicindustries.com/product/k0067.html

Craig