Possible Clues:

• Device first to be used if computer stops working?
• Something you flip in a house
• Toggle ... or a hint to 18-, 29- and 45-Across?
• Light controller—either of its first two words can precede either part of 17-, 25-, 51- and 61-Across
• Electric light option
• Remote button
• Two-way toggler
• Electrical device with a hint to answering 17-, 27- and 48-Across