Well Submersible Pump Wire Splice Kit Repair and Installation with Dual Wall Heat Shrink Tubing and Copper connectors for 4 Wires 10#12#14 AWG

These work great. You need to make the connection of the conductors first. I recommend crimping and soldering the metal connections. You will need to install the shrink part before joining the wires and move the shrink part away from the heating to make the joint. Once joined, then slide the shrink insulator over the joint and then shrink. I have only used a heat gun for heating. As the insulator shrinks you will see it so you can move the heat gun to get uniform shrinking. You do need to heat fully around the joint for best results. Toward the end of the heat shrink process you will see a material coming out under the heat shrink sleeve. This is normal and indicates there is a seal. A full seal will show no air bubbles in the joint area.