How to Replace a T12 Ballast? – A Comprehensive Guide


Written by

Thomas Carter



Marcos E. Williamson

how to replace a t12 ballast

T12 ballasts are older-generation ballasts that have been phased out since 2012. They are less efficient than newer ballasts and last less long too. So, there are plenty of reasons to switch them out. This detailed guide will teach you how to make the replacement.

Whether replacing T12 ballast with T8 or removing T12 ballast for LED fixtures, you can confidently complete the task once you learn how to replace a T12 ballast here.

We will walk you through all the specifics, like old ballast to (new ballast wiring). So, make sure you read everything until the end!

Ballast Replacement Guide: Remove, Then Install A Ballast In A Fluorescent Light

Changing a balast, regardless of whether it is a T12 ballast 2 lamp 8 ft replacement or a four-lamp 8ft T12 ballast replacement is a fairly straightforward task if you have the right tools and know the right steps to take. Below, we will provide you with all that you need.

Difficulty Level Duration Cost
1 out 5 (Beginner’s Level) About an hour or less $20 to $40

Step-by-Step to Replace a T12 Ballast

What You Will Need To Have:

  • A T12 light ballast replacement (either a T8 ballast or a LED light kit)
  • A wrench
  • A wire cutter
  • Wire connectors
  • A ballast wiring diagram (Optional; i.e., a 2 lamp t12 ballast wiring diagram)

Step 1 – Turn Off All The Power (Not Just The Light Switch).

The first thing you need to do to change a ballast on a fluorescent light is to turn off all the power. This guarantees that you will not get electrocuted during the process. Make sure that you switch the power off at your breaker, and not just flip your fixture’s switch.

Step 2 – Take Off The Cover Of The Light Fixture.


Next, remove the cover of the fixture to access the light tubes. Some covers will pop up with a bit of pushing on the sides, but some will require you to use tools. Typically, a socket wrench will be handy.

Step 3 – Remove The Light Tubes From The Light Fixture.

Once the cover is off, detach the light tubes from the fixture. All you need to do is turn the tubes clockwise until they are loosened in their sockets.

Slide the tubes out one end at a time, making sure to support them with your hand to prevent dropping and damaging them. Remember, these light tubes can explode and shatter!

Step 4 – Remove The Casing/Housing Of The Ballast.


Set the tubes aside somewhere safe to move onto the next lighting ballast replacement step: removing the casing or housing of the ballast. In most cases, you just need to squeeze the tabs on the sides to pull the cover off.

Step 5 – Disconnect The Wiring Of The Ballast & Remove The Ballast.


After detaching the cover, you will find the ballast along with its wiring. Then, disconnect the wires to remove the ballast.

If you are clipping the wires, make sure you do so close to their ends. Unscrew the ballast to detach it completely from the light fixture.

Then remove the two plates that hold the old sockets by poking your screwdriver into their edges and taking them out.

Step 6 – Install The New Ballast & Rewire Accordingly.

Now, you will be replacing old ballast with new electronic ballast by converting the old ballast to new ballast wiring.

Option 1 # Replace the T12 ballast with a T8 ballast.

  • Remove the wiring and all electrical components from the socket plates you took out in the previous step.
  • Your new ballast should have red and blue wires that are already stripped. But if not, use a wire stripper to remove an inch or so of the insulation on the cables, then run one stripped wire through each socket and slide each of these sockets into the connector slots on the socket plate.

You’re done wiring one end of the T8 ballast.


  • On the other end of the T8 ballast, there will be four wires: a white neutral, a black hot wire, and two yellow wires.
  • Trim off short sections of the two yellow wires so that you’ll have four cords instead of two.

Run each yellow cord through one socket, then wire the unattached ends of the short yellow wires through the sockets holding the long yellow wires.

You’ll have something that looks like this:


Proceed to slide the sockets onto their plate like you did previously.


  • Put the new ballast into place and screw to secure it. Position the socket plates back where you removed them, making sure the plates fit the notches on the ceiling or wall.
  • Remember the black and white wires we mentioned earlier? Use push connectors to link the black wire on the ballast to the black wire at the installation site. Do the same thing to the white wires. And you’re done!

Option 2 # Replace T12 with LED lights.

If you are switching to LED lights, you do not need to install a new ballast as they do not have one. You just have to bypass the ballast and move onto the next step.

First, pay attention to the power cord of the light. The green wire should go to the green screw or the ground. The black and white wires are the load and neutral, respectively.

If you look at the light ‘box’, there will be tombstones on each side of it. Take the wires on one tombstone side and connect them to the black or white wire.

The remaining wires on the other tombstones should be linked with whatever wire that’s left.

Step 7 – Reinstall The Light Tubes & Cover Of The Light Fixture.


After you wire ballasts in fluorescent lights, you can reattach the light tubes as well as the cover of the fixture, completing your light fixture ballast replacement.

There you have it! Your T12 ballast lights replace!

Frequently Asked Questions (FAQs)


1 – When would you replace a T12 ballast?

You might remove T12 ballast for LED lights or change T12 to T8. The former is a complete removal and conversion involving bypass, while the latter is a switch between an older-generation ballast and a newer one for improved efficiency.

2 – How long does a T12 ballast last?

A quality and well-maintained ballast can last up to 20 years. However, other factors can affect a ballast’s longevity, such as how often it is used and where it is used. For more information, check out our other article on “How Long Do Fluorescent Ballasts Last?”

3 – What is the cost to replace a T12 ballast?

It can cost between $20 and $40 if you do it yourself and from $75 to $150 if you seek help from an electrician. But the former’s cost can increase or decrease depending on the tools you already have.


How to replace a T12 ballast? Replacing a T12 ballast may seem like a daunting task. Still, with the right materials and some basic electrical knowledge, it can be done properly.

First, turn off the power supply to the fixture and remove the fluorescent tubes. Then, wire the new ballast or LED as instructed above.

Reinstallation of bulbs is necessary before switching back on power to verify that everything is working correctly. It is that simple!

Remember, if you are ever uncertain about anything while repairing your fixtures, feel free to seek professional assistance for your own safety.

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