Mustang MSD 6AL Ignition Box (1965-1995) Installation Instructions

Tools Required:
  • Power Drill
  • 3/16 inch Drill Bit
  • Screw Driver/Sockets to Match Bolts
  • Ratchet
  • Wire Cutters
  • Wire Strippers
  • Wire Crimpers
  • Wire Connectors
Install Difficulty:
  • Moderate
  • Moderate Project
1. To begin the installation of your new Mustang MSD 6420 6AL Ignition Box, inspect the box and the part for damaged or missing parts.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
2. Disconnect the negative cable from your Mustang battery. Read over the instructions that are included in the package to familiarize yourself with the process, then locate a suitable area to mount the MSD ignition box, which can either be in the engine bay or inside of the car.
3. I decided to mount my box in the Mustang interior, under the passenger seat. After locating the perfect spot, put the MSD ignition box in place to use the mounting holes to mark exactly where you will be drilling.
Mustang MSD 6AL Ignition Box Install Image
4. Drill a 3/16 inch hole in the four mounting locations you just marked.
5. Use the supplied vibration mounts to mount the MSD box in its desired location. Since mine is mounted inside of the car, I opted to use my own screws to secure the box to the floor pan.
Mustang MSD 6AL Ignition Box Install Image
6. Find a good location to attach the ground wire and run the thick black wire coming from the MSD box there and attach it. For my grounding location, I chose the mounting nut for the relay box located under the passenger seat.
Mustang MSD 6AL Ignition Box Install Image
7. For my particular engine (from Ford with electronic fuel injection), the magnetic pickup on the Mustang ignition box, which has purple and green wires together, is not used. Simply leave this wire alone, and leave the connection wire for it in the box.
8. All of the other wires will need to be routed to the coil, battery, and starter area. On my car, I fed the wires through the firewall on the passenger side where the computer harness is located.
Mustang MSD 6AL Ignition Box Install Image
9. Once they're through that hole, feed the wires through a loom around the back of the firewall and across the Mustang shock tower on the driver side.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
10. Connect the heavy red wire from the MSD ignition box to either the battery or the starter solenoid.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
11. There are two wires that will go into the plug on the ignition coil and will need to be cut. The small red wire from the ignition box will need to be connected to the positive wire coming from the vehicle’s ignition. Strip the positive wire and use a connecter to crimp that small red wire to the positive wire.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
12. 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.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
13. Use a connector and crimp the white wire from the Mustang ignition box to the negative wire coming from the vehicle’s ignition.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
14. Crimp the black wire from the MSD ignition box to the negative wire coming from the plug on the Mustang ignition coil.
Mustang MSD 6AL Ignition Box Install Image
Mustang MSD 6AL Ignition Box Install Image
15. At this point you have all of the wiring connections finished. On the MSD ignition box, flip open the silver rectangle that states “REV”. There are two turn dials under the rectangle. Turn the first dial with a screw driver to the number (in thousands) where you would like the rev limiter to be set at. Turn the second dial to the number (in hundreds) where you would like the rev limiter set at. For example, my first dial is set at 6 for 6,000 and the second dial is at 3 for 300 resulting in a rev limiter of 6,300.
16. Look over your work and make sure all of the wiring is in a safe location.
17. Reconnect your negative battery cable and enjoy your new Mustang MSD 6AL Ignition Box.