Turn power to the line off at the breaker panel.
Separate the components of the waterproof splice kit.
Insert the end of one cable into one of the covering sides, then insert the other cable into the other half of the covering.
Strip the covering off 1/2 inch of each wire.
Insert the wires into the slots on the metal inner splice piece. Match each wire up with the same color wire from the second cable. For example, insert the end of the red wire, then in the slot on the opposite side of the metal splice insert the other red wire so the two meet up.
Tighten the screws on the side of the metal splice so they grip the wires tightly, then slide the two pieces of waterproof covering together over the splice and connect the halves to create a waterproof seal.
Turn the power back on and ensure no problems exist before burying or attaching the connector permanently.