If you refuse to do it right with soldering and heat shrink, get some 3M silicone electrical tape like below. They make it in 7-mil thick, 12-mil and 20-mil thick. This stuff has no adhesive on it and uses the properties of silicone bonding to itself rather than relying on adhesive that degrades over time.
7-mil price per case of 12:
12-mil
20-mil
7-mil price per case of 12:
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12-mil
3M Silicone Electrical Tape, 70, Scotch, 1 in W x 30 ft L, 12 mil thick, Gray, 1 Pack 70 | Zoro
Order 3M Silicone Electrical Tape, 70, Scotch, 1 in W x 30 ft L, 12 mil thick, Gray, 1 Pack, 70 at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.
www.zoro.com
20-mil