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MSD 6421 6AL-2 CDI Ignition Box
MSD 6421 6AL-2 CDI Ignition Box

MSD 6421 6AL-2 CDI Ignition Box

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MSD 6421 6AL-2 CDI Ignition Box
MSD 6421 6AL-2 CDI Ignition Box
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Part # 5476421
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  • Get FREE shipping when your order includes this item and exceeds $99! Ground shipping only in the contiguous US.


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The all new 6AL-2 capacitive discharge ignition will easily connect to nearly any 12-volt negative ground distributor system. Inside the new cast aluminum housing youll find an advanced micro-controller that manages the timing and rpm of the ignition.

  • Upgraded digital spark output versus standard 6AL series
  • Multiple sparks over 20° of crankshaft rotation ensures complete combustion
  • Blast off the starting line with the 2-step rev limiter 
  • High end overrev protection plus clutch or transbrake launch limiters
  • Adjustments made via four rotary dials in 100 RPM increments
  • Accepts Hall-effect, points and mag pickup triggers

547-6421 Instructions (PDF)

Learn more about determining the proper MSD ignition control box for your application by reading our tech article. The Differences Between 6 Series MSD Ignition Control Units.



  • Spark Energy:  135 mJ per spark
  • Primary Voltage:  535 Volts
  • Secondary Voltage:  45,000 Volts
  • Spark Series Duration:  20 degree Crankshaft Rotation
  • RPM Range:  12,500 RPM with 14.4 Volts
  • Voltage Required:  12-18 Volts, Negative Ground
  • Current Draw:  .7 Amp per 1,000 RPM
  • Weight and Size:  3 lbs., 7"L x 4"W x 2"H


For warranty information, visit
Some parts are not legal for use in California or other states with similar laws/regulations

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Videos & Articles
  • Looking for an easy performance upgrade to your ignition system? MSD's line of Ignition Control Boxes offer extreme improvements to drivability and high rpm applications. Here's a look at the differences between the 6 series line-up.
  • Want to upgrade the HEI your old motor came with? Here is some advice!
  • Speedway Tech Zach discusses the Pertronix Ignitor III conversion in his '55 Chevy.
  • In preparation to transplant a 430hp 383 stroker into Project Chevelle, Zach R. made up a set of plug wires for the car. To keep it nice and tidy they needed to be routed just right, be the perfect length and not distract from the engine!

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