Cut four wires to length to fit the relay circuit. Crimp wire connectors to fit the relay pins and route one wire to the switch that is used to operate the object being installed, such as lights or a power antenna. Plan to cut the wire lengths accordingly and keep in mind that the relay is normally hidden, located under the dash or hood, and protected for the elements.

Disconnect the negative terminal on the car battery. Cut another wire and crimp on connectors. Run the prepared wire from the fuse box to the dash mount switch that controls the relay switch. Be sure and use a test light and locate power with the key on in the fuse box.

Wire the relay coil according to the diagram that is normally imprinted on on of the side of the relay housing. One wire is used to ground the relay coil. The coil is an electromagnet. When power is applied to the coil from the dash switch, the magnet energizes and a movable arm inside the relay is attracted to the magnet. When this arm pulls down, it closes a set of contacts and power flows through them. Install a ground wire to one of the relay coil pins and the dashboard switch wire that supplies power to relay coil to the remaining relay coil pin.

Wire the object with power that is controlled by the relay. Crimp an in-line fuse into the battery power supply wire, making sure it is near the battery. This protects the new object that is installed. On the side of the relay the power-in and power-out pins are shown with the movable arm. Install the supply power from the battery to one of the pins with one of the prepared wires, and use the last prepared wire to supply power from the remaining pin to the new object that is installed. Run this wire from the power-out pin on the relay and crimp it to the positive wire on the new object that is installed.

Ground the last remaining wire - the new object ground wire - to the car negative circuit. Reconnect the battery. Operate the dashboard switch and the relay will click as it is energized. Battery power will flow through the relay contacts that are in the closed position and operate the new object. Turn the dashboard switch off and the relay contacts open and the object turns off.