1965-1995 Mustang MSD 6A Ignition Box Install

1965-1995 Mustang MSD 6A Ignition Box Install

Last Updated December 19, 2023 | Nate Moonis

It's common for your 1965-1995 Mustang to not spark as effectively or efficiently as it ages. This can cause your ride to run poorly and miss out on power. This can be caused by fouled spark plugs, insufficient current reaching the spark plugs, and other potential spark issues. Help your 1965-1995 Mustang run at its best by adding an MSD 6A ignition box.

How to Install an MSD Ignition Box in a 1965-1995 Mustang

Installing an MSD 6A ignition box in a 1965-1995 Mustang is a moderately difficult process that requires you to have some knowledge about wiring including how to properly connect and crimp wires. You'll also need to creatively route multiple wires throughout your Mustang depending on where you mount the ignition box.

It's important to note that this guide is meant for use with the MSD 6A red ignition box and won't necessarily work with other units/brands. The steps and the wire colors mentioned below will be different if you decide to install a different unit.

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Tools Needed

  • Power Drill
  • 3/16" Drill Bit
  • Screwdriver/Sockets to Match Bolts
  • Ratchet
  • Wire Cutters
  • Wire Strippers
  • Wire Crimpers
  • Wire Connectors

Step 1: Disconnect Negative Battery Terminal

Open the hood and disconnect the negative battery terminal to prevent any shorts or electrical issues from occurring during the installation.

Step 2: Locate Mounting Area

Read the instructions that come in the MSD ignition box packaging, then locate a suitable area to mount the box. This can be in your car's engine bay or interior. We chose to mount ours under the passenger seat of our Mustang.

The MSD ignition box in its open packaging

Step 3: Mock Up Mounting Holes

Set your MSD ignition box into place on the mounting area you found in the previous step. Once you have it properly situated, mark where the mounting holes on the ignition box are located in the mounting area to determine where you'll need to drill.

The MSD ignition box mounting area mocked up under the passenger seat of a Mustang

Step 4: Drill Holes

Use your drill and 3/16" drill bit to drill four holes in the mounting locations you just marked.

Step 5: Mount the Ignition Box

Mount the ignition box in your desired location using the vibration mounts supplied within kit. We used our own screws to secure the ignition box to the floor pan.

A mechanic tightening down the ignition box mounting brackets with a screwdriver

Step 6: Ground the Ignition Box

Find a good grounding location on bare metal without any paint or rust for the strongest ground possible. Then, attach the black ground wire coming from the ignition box to the grounding location and secure it properly. We attached the ground wire to the mounting nut on the relay box under the passenger seat.

A diagram showing where to route the ground wires on the MSD ignition box

Step 7: Route Ignition Box Wires

The magnetic pickup on the ignition box is not used for the engine in our Mustang (Ford V8 with electronic fuel injection). Leave the purple and green wire alone and leave the connection wire in the box.

Route the rest of the wires to the coil, battery, and starter area respectively. We fed the wires through the firewall on the passenger side where the computer harness is located. This routing process will be different depending on where you mounted your Mustang ignition box.

A diagram showing where to route the ignition box wires in the engine bay

Step 8: Feed Wires Through Loom

Tap into the wire loom along the back of the wire wall and route them across the Mustang shock tower on the driver's side.

A diagram showing where to feed the wires once they're in the engine bay loom

A diagram showing where to feed the wires once they're in the engine bay loom

Step 9: Connect Red Wire

Connect the heavy red wire from the Mustang ignition box to either the battery or the starter solenoid.

A diagram showing where to connect the heavy red wire in the engine bay

A diagram showing where to connect the heavy red wire in the engine bay

Step 10: Strip and Connect Ignition Box Wires

There are two wires that go into the plug on the ignition coil. They will need to be cut. Connect the small red wire from the ignition box to the positive wire coming from the vehicle's ignition. Strip the positive wire and use a connector to crimp the small red wire to the positive wire.

A diagram showing which wires to strip and which wires to connect on the ignition box

A diagram showing which wires to strip and which wires to connect on the ignition box

Step 11: Connect Orange Wire

Connect the orange wire from the MSD ignition box to the positive wire coming out of the plug on the ignition coil by crimping them together with a connector.

A diagram showing where to connect the orange wire in the engine bay

A diagram showing a mechanic crimping the orange wire after it's been connected properly

Step 12: Connect White Wire

Crimp the white wire coming from the Mustang ignition box to the negative wire coming from the vehicle's ignition with a connector.

A diagram showing where to connect the white wire in the engine bay

A diagram showing a mechanic crimping the white wire after it's been connected properly

Step 13: Connect Black Wire

14. Crimp the black wire from the ignition box to the negative wire coming from the plug on the Mustang ignition coil.

A diagram showing where to connect the black wire in the engine bay

A diagram showing a mechanic crimping the black wire after it's been connected properly

Step 14: Set Rev Limiter

After you've connected all of the wires, flip open the silver rectangle that says "REV". There should be two dials underneath the rectangle.

Turn the first dial with a screwdriver to the number (in thousands) where you'd like your rev limiter to be set. Then, turn the second dial to the number (in hundreds) where you'd like your rev limiter to be set. For example, we set our first dial to 6,000 and our second dial to 300 for a rev limit of 6,300 RPM.

Step 15: Reconnect Negative Battery Terminal

Reconnect your negative battery terminal and check for any loose connections on your battery.

Congratulations, you're all done!

Experience Efficient Ignition and Improved Power

With a new MSD ignition box, you're able to effectively monitor and control every firing and rev limit. This allows for improved efficiency and increased power. While not right for every enthusiast, the MSD ignition box might be the right choice for your Mustang if you're looking to customize every little detail of your ride.

If you're interested in purchasing an ignition box for your Mustang but aren't sure if the MSD 6A ignition box is for you, check out our selection below. You're sure to find one that fits your needs and vehicle.


This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about CJ's editorial standards and guidelines.