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Electrical Wire and Cable

Add a Switch and Connecting the Wires

How Can I Add a Light Switch to the Existing Circuits? Adding Light Fixtures and a Light Switch to Existing Circuit Wiring, The Most Common Mistakes When Adding an Additional Light Switch and How to Fix Them.

Home Electrical Wiring Video

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Adding a Light Switch
Electrical Question: How Can I Add a Light Switch to Existing Circuits?

I have a switch box with two light switches. Each switch controls separate light fixtures, however one switch apparently draws power from the other switch.

I have tried to add an additional switch to one of the existing switches. Here is the wiring that I have to work with:

The new line is attached to a three way switch in the original box where there is a red and white wire to the switch, and black to the white from the 2-wire line from the appropriate light source. The black from that line is attached to the three way switch and power from the other switch. The other 3-wire cable is hooked up similarly where the red and white connect to the switch, and the black to the black of one of the light source (or power) 2-wire cables. The two whites of the two 2-wire lines from the light source are connected, and the final black from the 2-wire lines from the light sources (or power) is connected to the second three way switch.

The downstairs or other light source works but the new three way and its companion in the old box do not light the upstairs light source as intended.

Can you offer any direction? I have tried a number of different connections and either get a flipped breaker or still just the two light sources and not the third which is the one I wish to add a switch to.


Background: Rolly, a Homeowner from Indianapolis, Indiana.

Dave’s Reply:
Thanks for your electrical wiring question Rolly.

Connecting the Wires for a Switch

Application: Wiring Additional 120Volt Light Fixtures and Light Switches.
Skill Level: Intermediate to Advanced – Best installed by a Licensed Electrician.
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 existing circuit, turn it OFF and Tag it with a Note before working with the wiring.
Notice: Installing additional light switch wiring should be done according to local and national electrical codes, with a permit and be inspected.
Materials: Make sure light switches have the same amperage and voltage rating as the existing light circuit, and the switch is fully compatible with the light fixture and the type of light bulbs that will be used.

Adding a Light Switch or Light Fixtures to Existing Circuit Wiring

It is important to define your project to fully understand the wiring requirements and connections. For example, this electrical question does not describe if an additional switch will be used for existing lights, or if the new switch will control a new light fixture. However, I will discuss both the basic requirements for adding a light switch and adding light fixtures to existing circuit wiring.

Adding a Light Switch

Electric Wires Required when Adding a Light Switch

Adding Light Fixtures and a Light Switch

Electric Circuit Requirements when Adding a Light Switch and Light Fixtures

Basic Circuit Wiring Commonly Found in an Existing Switch Box

Troubleshooting Light Switch Wiring Problems

Wiring an additional switch incorrectly can cause a variety of results and possible circuit problems. Many of these problems occur when the existing circuit wiring is not fully understood or identified resulting in incorrect wire connections to the switch or light fixture circuit cable. The following will explain problems and solutions for many common switch wiring problems.

The Most Common Mistakes When Adding a Light Switch and How to Fix Them

Problem: The Circuit Breaker Trips Off when the Power is Turned On or the Light Switch is Turned On.

Problem: The New Light Switch and Light Fixture Only Work When Another Switch is On.

Problem: The New Light Switch and Light Fixture Works When Other Light Switches are Turned On or Off.

Problem: The New Light Switch and Light Fixture Does Not Work At All.

Conclusion and Summary

The Key to Light Switch Wiring is to identify all the circuit wires involved and understand what their function is within the circuit and light fixture switching process.

I have provided the following resources that lead to fully detailed information that will further assist you with wiring light switches.

More about Light Switch Wiring

Light Switch Wiring
Light Switch Wiring
Wiring Diagrams for Light Switches
Fully explained pictures and wiring diagrams about wiring light switches describing the most common switches starting with photo diagram 1.

This link is helpful as a Homeowner
Do-It-Yourself Electrical

Home Wiring Diagrams
Wiring Diagrams

The following may also be helpful for you:

Dave's Guide to Home Electrical Wiring:

» You Can Avoid Costly Mistakes! «

Here's How to Do It:
Wire It Right with the help of my Illustrated Wiring Book

Great for any Home Wiring Project.
  electrical wiring  

Complete Guide to Home Electrical Wiring

Perfect for Homeowners, Students,
Handyman, Handy Women, and Electricians
Wiring GFCI Outlets
Wiring Home Electric Circuits
120 Volt and 240 Volt Outlet Circuits
Wiring Light Switches
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
NEC Codes for Home Electrical Wiring
....and much more.

Learn more about Home Electrical Wiring
with my Online Video Course:
Basic Home Electrical Wiring by Example

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

Electrical Tips to Help You Wire it Right

The Safest Way to Test Electrical Devices and Identify Electric Wires!

The Non-Contact Electrical Tester
This is a testing tool that I have had in my personal electrical tool pouch for years, and is the first test tool I grab to help identify electrical wiring. It is a Non-contact tester that I use to easily Detect Voltage in Cables, Cords, Circuit Breakers, Lighting Fixtures, Switches, Outlets and Wires. Simply insert the end of the tester into an outlet, lamp socket, or hold the end of the tester against the wire you wish to test. Very handy and easy to use.

The Quickest Way to Check for Faulty Electrical Wiring!

The Plug-In Outlet Tester
This is the first tool I grab to troubleshoot a problem with outlet circuit wiring. This popular tester is also used by most inspectors to test for power and check the polarity of circuit wiring.
It detects probable improper wiring conditions in standard 110-125 VAC outlets Provides 6 probable wiring conditions that are quick and easy to read for ultimate efficiency Lights indicate if wiring is correct and indicator light chart is included Tests standard 3-wire outlets UL Listed Light indicates if wiring is incorrect Very handy and easy to use.

Strip Off Wire Insulation without Nicking and Damaging the Electric Wire!

The Wire Stripper and Wire Cutter
My absolute favorite wire stripping tool that I have had in my personal electrical tool pouch for years, and this is the tool I use to safely strip electrical wires.
This handy tool has multiple uses:
The wire gauges are shown on the side of the tool so you know which slot to use for stripping insulation.
The end of the tool can be used to grip and bend wire which is handy for attaching wire onto the screw terminals of switches and outlets..

The wire stripper will work on both solid and stranded wire. This tool is Very Handy and Easy to Use.

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FAQs Frequently Asked Questions and Comments

2 Responses to “Add a Switch and Connecting the Wires”
  1. Jade Starton says:

    Thanks for posting this. Even knowing some great electrical contractors in Indianapolis and midland electric supply it’s nice that my uncle can search online and not have to go to them for every little thing. I’m not saying though that messing with wires is a little thing! But the more he can do on his own, the happier he is.

  2. Dave Rongey says:

    Your Welcome Jade,
    I’m glad I can be of assistance for your Uncle’s home electrical wiring projects, and if he gets in over his head I’m sure you guys will lend a helping hand as well.