Eventronic 4:1 Heat Shrink Tubing Kit - 400 Pcs Adhesive Lined, Wire Shrink Wrap Tubing, Marine Grade Industrial Heat-Shrink Tubing, Black and Red, for Father's Day Gifts

Also, for a good insulation, before you actually solder the wires to the connector, ideally you can put a "heat shrink tubing" on the wire first, then once both connectors are soldered, put the tubing over the solder joints parts, and apply heat (either with the soldering iron, or hair dryer) on it so that it tightly wraps around the solder joints. This will give it a professional look, but also better insulate it from contact with the nearby connector, water, or any other conductive material that might come into contact. Of course, worse case you can always use electric tape ! Amazon link for reference: https://www.amazon.com/Eventronic-Shrink-Adhesive-Industrial-Heat-Shrink/dp/B0DK34NL18/ref=sr_1_6?sr=8-6BUT you can probably find a smaller amount online or at a nearby electronics shop.