A neon sign is more than just the neon tubes. It also contains a transformer, or power supply, that turns the alternating current into direct current to excite the neon gas. However, this transformer must be individually wired into the sign since most neon signs are custom made. The process is intimidating at first but you do not need to be an electrician to wire a neon transformer as it is designed to just plug into the neon tubes.
Screw the neon transformer to the back of the neon sign if applicable (if not, skip to Step 2). Some smaller signs will have the power transformer attached directly to the sign, while larger neon signs will have the transformer sit apart from the sign. If the transformer is meant to attach to the sign, place the transformer against the back of the neon sign so that the screw holes on the side flanges line up with the screw holes on the back of the sign. Thread all four of the screws in by hand first to secure the transformer, then tighten the screws down with a screwdriver until the screws are flush with the backing.
Take the two individual power wires (not the power cord that goes into the wall socket) and thread them through the two holes in the back of the sign -- one for each wire. Pull each wire toward opposite ends of the neon tube. Take the caps off the ends of the tubes.
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Strip a quarter-inch from the end of each power wire if the wires do not come pre-stripped. Twist the exposed wires with the exposed wires at the end of each neon tube. Twist the wires tight and at least three times around to ensure the connection is good. Having to rewire a neon sign can get tedious after a while. Put the caps back on the ends of the neon tubes with the power wires underneath.
Plug the power cord (the one with the socket plug on it) into a nearby wall outlet. Flip the power switch on the neon transformer and check to make sure the neon tube lights up. If not, turn the sign off and unplug the power cord, as you need to rewire the power wire leads onto the neon tube wire for a better connection.