LED lights are designed to operate on low-voltage direct current similar to that supplied by batteries. To wire LED lights to 120-volt household current, a "step down" transformer is required to convert the alternating current into the lower voltage direct current. While there are sets of LED light that are pre-wired with a DC transformer that is simply plugged into a 120-volt electrical outlet, for customized light installations you must wire a transformer between the LED lights and the 120-volt power source.
Things You'll Need
Shut off the power to the 120-volt circuit that the LED lights will be connected to.
Insert the end of one wire coming from the LED lights and one wire coming from the DC side of the transformer into opposite ends of a wire connector. Fasten in place by crimping the connector closed with the pliers.
Insert the remaining wire from the LED lights and the remaining wire coming from the DC side of the transformer into opposite ends of a wire connector and crimp closed with the pliers.
Attach the hot (black) wire on the AC side of the transformer to the hot wire of the 120-volt AC circuit by inserting the ends of both wires into a wire nut. Twist the wire nut onto the wires with your fingers until tight.
Insert the end of the neutral (white) wire from the AC side of the transformer and the end of the neutral wire of the 120-volt AC circuit into a wire nut. Twist the nut tight with your fingers.
Turn on the power and test the lights.