Replacing an Old Switch with a Dimmer Switch

By Dave Rongey - Summary:

How to Connect Circuit Wiring for a Light Switch or Dimmer Switch: Identifying Old Electrical Wires, Wiring the Dimmer Switch, 3 Way Dimmer Switch Wiring Diagram.

How to Replace an Old Switch with a Dimmer Switch

Electrical Question I am trying to replace an old light switch and install a dimmer.

  • The old light switch has 3 wires connected to them.
  • One wire has copper-colored braiding connected to the top screw terminal and the bottom screw terminal has 2 blue-colored copper wires connected to it.
  • The black screw terminal on the old switch has no wire connected to it.
  • None of the wires are labeled. How do I identify the wires and continue with the installation?

This electrical question came from: Anthony, a Student from New York, NY, Alabama.

Dave’s Reply:
Thanks for your electrical question Anthony.

Electrical Answer

Electrical Wiring Connections for a Light Switch and Dimmer Switch


  • Skill Level: Beginner to Intermediate.
  • Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
  • Estimated Time: Depends on personal level experience and ability to work with tools.
  • Precaution: Identify the light circuit, turn it OFF and Tag it with a Note before working with the wiring.
  • Notice: Installing additional fixture wiring should be done according to local and national electrical codes with a permit and be inspected.
  • Materials: Make sure the replacement light switch has the same amperage and voltage rating as the original switch, and is fully compatible with the electrical circuit, the light fixture and the type of light bulbs being used.


How to Connect Circuit Wiring for a Light Switch or Dimmer Switch

  • Light Switch Wiring Connections
    • The incoming power.
    • An outgoing wire to the light fixture.
    • White neutral wires that are spliced together with a wire connector.
    • A ground wire attached to the frame of the switch.
    • NOTE: There could be another outgoing power line attached as well, however an additional wire should not be attached to the the switch but rather connected through sing a splice and pigtail.
  • Identifying Old Electrical Wires
    • The best way to identify old electrical wires is by using a voltage tester and testing to a grounded source.
    • In most cases the neutral wire of old cloth electrical wire did have a white colored insulation.
    • For some older homes the neutral wires were connected to the switches, not the hot wires.
  • Wiring the Dimmer Switch
    • Modern conventional dimmer switches do not use neutral wires so the wiring must be identified and connections may need to be made in order to make sure the correct wires are being connected to the dimmer switch.

Additional Resources about Wiring Dimmer Switches and Light Switches

3 Way Dimmer Switch Wiring Diagram
Fully explained 3 way dimmer switch wiring diagram will take the mystery out of wiring a 3-way dimmer switch.

Learn How to Wire it Right with my
Complete Guide to Home Electrical Wiring
Perfect for Homeowners, Students,
Handyman, Handywomen, and Electricians
Wiring GFCI Outlets
Wiring Home Electrical Circuits
120 Volt and 240 Volt Outlet Circuits
Wiring 3-Wire and 4-Wire Electric Range
Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet
How to Troubleshoot and Repair Electrical Wiring
Wiring Methods for Upgrading Electrical Wiring
Electrical Codes for Home Electrical Wiring
....and much more.

» Click here to learn more about Home Electrical Wiring «
  repair electrical wiring  

Be Careful and Be Safe - Never Work on Energized Circuits!
Consult your Local Building Department about Permits and Inspections for all projects.


Click the banner to Ask a Detailed Electrical Question and get an Instant Reply:
electrical question


If you are asking a Quick Question please make sure it is about This TOPIC:
“Replacing an Old Switch with a Dimmer Switch”

Comments Posted here are Open for Quality Discussion and Participation.