Inspect the power converter. Some converters have an outlet plug on one end and can be plugged directly into a residential receptacle. Converters that do not have outlet plugs should have the 120 volt terminals clearly labeled.
Connect the black, or hot, wire of the power source to one of the 120 volt terminals. Connect the white, or common, wire to the remaining 120 volt terminal.
Look at the other side of the converter. Determine which of the 12 volt terminals is negative. This should be marked on the converter.
Connect the negative wire of the device that the converter will power, usually a black wire, to the negative output terminal of the converter. Connect the positive wire, usually red, to the positive output terminal of the power converter.