Fix possible for broken insulation of wires at the alternator?

Another option for insulating bare wires on location.

https://www.gardnerbender.com/en/p/LTB-400/Liquid-Electrical-Tape-Werpro-Seal

Yes as a general rule you want strain relief where the wires attach. Anything that forms a solid attachment runs risk of just moving the stress point further along the wires. A good blob of automotive silicone sealant or the rubberized liquid E tape should make durable yet flexible strain relief.