Teague On Tech: Q & A with Bob Teague Sept/Oct 2022

As seen in Speedboat Magazine’s
Sept/Oct 2022 Issue.

MSD Ignition Box

Dear Bob:

Q. I have a 27’ Eliminator Daytona that eats
MSD 6AL ignition boxes. I have owned this
boat nine years and I have had six MSD 6AL
ignition boxes fail in that time. My boat is
not some high tech “Space X Raptor thing.” It is just a Dart big block with a Delphi ECM and a Whipple quad rotor system. The drive
is an IMCO with the dual down shaft. The prop is a five-blade.

I noticed that you put the MSD boxes on a mount on the front of your engines. I am
wondering if the reason is heat related. I think it looks better on the rear of the motor.
Mine is on the back of the engine on a billet bracket. I checked and changed the coil,
ignition wires, power cables, and grounds, but not the mounting location. I am still
having the problem.

Should I consider relocating the MSD box or do you think that I am cooking the ignition
box for some reason. Please help!

Carter Pasch
Garden Grove, CA

The MSD 6AL ignition box in intended for automotive use. They are typically red in color. The correct MSD box to use in marine applications is the part number 6M-2L. The marine version of the MSD box is sealed internally and comes with moisture tight electrical connections. The rev-limiter also plugs into a water-tight harness. The automotive version is not sealed and the rev-limiter chip plugs into the side of the box.

We have bracket kits that can mount the MSD 6M-2L box on the end of either cylinder head. Typically, on carbureted engines, the MSD 6M-2L box is mounted on the cylinder head behind the number 8 cylinder. This is because we mount the oil filter and system on the rear of the head behind the number 7 cylinder. This is a convenient place for the box mounting which is close to the distributor, engine harness, and coil.

MSD 6M-2L ignition box.

We have found that mounting the MSD box close to the ECM can cause weird interference with the computer. For this reason, and because there is no nice way to install the MSD box at the same location as the assembly that holds the computer, relays, circuit breaker, solenoid, IAC’s, etc., the box is moved to the front of the engine.

The box should not be mounted where it is exposed to excessive heat. If it is mounted on the engine, the mounting bracket should be spaced to provide an air gap, so the engine heat is not directly conducted to the box.

The most common cause of MSD box failure is related to poor installation, wiring, or alternator problems. An alternator with a faulty diode can create a problem. The constant power supply that is connected to the battery (usually on the main starter post) directly or indirectly cannot be interrupted while the engine is running. For example, if you change the position of certain battery switches, or turn it off while the engine is running, it will likely damage the ignition box. This is because the alternator will create a voltage spike that burns out a fuse link in the box. A similar scenario can be created by a poor main ground connection.

To test the box if you are using an MSD distributor, you can unplug the wire to the distributor and jump the two contacts on the lead going to the box with the ignition on to test the box. This should fire the box. Alternatively, you can unplug the signal wires from the distributor and touch the small white wire to ground (any metal place on the engine) with the ignition on to fire the box. If the box does create a spark with these tests, the problem is somewhere else. The next place I would check is the magnetic pickup or module. A faulty module can damage the MSD box.

The MSD 6M-2L box has a separate output wire (gray in color) for the tachometer signal. This is a better source to connect to an analog tachometer than the ECM output. If you used the MSD tach wire, you must disconnect the tach wire in the harness that gets its signal from the ECM. Occasionally, a faulty tach can cause problems with the ECM or MSD box.

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