Wire Connector For Heated Blanket
I'd inline splice &amp; solder it, then heatshrink.

Use some heat shrink tubing, spread the wire enough to hold the heat shrink.
inline wrap the wire to its mating side so that it stays flush in the lengthwise of the wire, then solder it.
Then heat shrink each over the repair.

This will reudce the likelyhood it pulls apart, keeps out moisture, and is electrically safe.

This is not 100% how I explained it, but google inline splice wire, and you will see numerous pictures to get the idea:
https://www.instructables.com/id/Soldering-Tutorial-Inline-Splicing/