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Unilite, MBI and E-Spark: The Real Deal

I hear so many myths and partial truths about Mallory ignition modules that I thought I'd try posting the facts on a the forum to clear things up.

Mallory has three types of modules (not including the new rev limiting HEI module) that fit inside the distributor: Unilite, Magnetic Breakerless Ignition (MBI) and the new E-Spark. The Unilite and E-Spark are similar but the E-Spark is manufactured on automated equipment to reduce manufacturing costs so that the E-Spark conversion kits can be sold at about the same price as a Pertronix. The MBI uses a similar circuit but uses a magnetic pickup as a triggering device rather than an optical pickup.

The Unilite and the MBI are available in complete Mallory distributors. The Unilite and the E-Spark are available in conversion kits for stock type point distributors.

All three modules were originally designed to replace point style ignitions. Point style ignitions use coils with high primary resistance and ballast resistors (or resistor wires such as used in AMC, Ford and GM). Thus, the Mallory modules were designed to use a ballast or resistor wire.

Unilite, MBI and E-Spark modules (and Pertronix) are basicly electronic replacements for points. They are not amplifier boxes like a Hyfire or an MSD box. They are simply a way to get rid of the points. The spark output is usually a little higher than points due to the increased dwell time (and you don't have to worry about point bounce) but the output is not significantly greater than points. HEI type modules or external amplifier boxes are the only way to significantly increase spark output.

All three Mallory modules wire the same way. There are three wires:

The brown wire is grounded to the engine. Make sure you also have a good ground cable/strap between the engine and the frame/battery. Do NOT ground the brown wire from the module directly to the frame or battery. If you do, the brown wire will become a ground for the starter during cranking which will melt the brown wire and take out the module.

The green wire connects to the negative side of the coil.

The red wire can connect to the positive side of the coil but it's better to connect it to the high side (12 volt) side of the ballast resistor. Remember, the ballast or resistor wire is there to limit the current through the coil and the green wire. The red wire prefers to see full battery voltage. If you connect the red wire to the positive side of the coil (which is also the low side of the ballast) the engine may not start as easy especially if the battery is low. If your car has a resistor wire rather than a ballast, you can either hook it to the positive side of the coil, or better yet, find a place to hook it that will feed the red wire full battery voltage whenever the key is on.

If you are also using an external box such as a Hyfire or MSD, follow the wiring instructions that come with the box as the module will need to be wired differently. A ballast or resistor wire is not needed when using an external box since all the current for the coil goes through the box rather than the module. (When used with an external box, modules and points last almost forever because very little current goes through them). Some people like to leave the ballast or resistor wire in place when hooking up an external box (it won't hurt anything) so that if the box fails you can bypass the box and still get home running on the module alone.

I often hear people ask what voltage they should have at the coil when running a Mallory module without an external box. The standard answer is about 7 to 10 volts measured at the coil with the engine running. However, while this is easy to measure, it is not the best thing to measure since the voltage will vary depending on the voltage output of the alternator. What really matters is the total resistance of the primary side of the ignition. This includes the ballast (or resistor wire) and the primary resistance in the coil (measured with an ohm meter between the positive and negative terminals on the coil). The ideal total resistance is a minimum of 1.4 ohms and a maximum of about 3.5 ohms. More than 3.5 ohms is safe for the module but the spark may be too weak for optimum performance. Use an ohm meter to measure the resistance across the ballast and add that to the amount of primary resistance in the coil. The total should be between 1.4 and 3.5 ohms. You may need to measure the resistance of the ballast after it has warmed up since some ballast resistors increase in resistance with temperature. If your car has a resistor wire rather than a ballast it can be difficult to measure the resistance in the wire as the wire gets lost in the harness. If so, assume that the resistance in the wire is about 1.0 ohms which is typical.

Some coils have so much primary resistance that a ballast resistor or resistor wire is not necessary. Mallory has two new Promaster coils that have all the resistance built into the coil (29450 and 30450). Using these coils, no additional resistance is needed.

Having all the resitance built into the coil has drawbacks however. The coil will run hotter which will reduce the life of the coil somewhat. Also, high resistance coils are not recommended for use with external boxes as the coils will overheat and fail (sometimes even explode!).

Don't use solid core plug wires with any electronic igntion.

If you weld on the car, disconnect the module before doing so.

Unlike popular opinion, the standard Pertronix module also requires a certain minimum resistance. When using a Pertronix on a car that was using points, no ADDITIONAL resistor is needed, but this is also true for Mallory modules. Pertronix also sells their own coils with high resistance so that a ballast is not needed.

Now you know the real deal.

RobbMc - Engineer at Mallory Ignition/Erson Cams/Accel Ignition

The best coil to use with the Hyfire VI is the 29625. It will allow the engine to rev to around 10,000 rpm. However, if you are never going to rev over 8000 rpm, the 29440 coil will work just as well. Plus the 29440 coil can be used with stock electronic ignitions, Unilites, etc in case you ever want to use the coil with a different ignition. The 29625 must be used with a CD box of some kind. I ran a 29625 with a Hyfire. Worked great. But when I loaned the Hyfire to someone and tried to drive home on the MBI module alone, the engine would not start. I had to install a 29440 to run without the box. The 29440 is nice because you can run it with or without the box. The 29625 will make a hotter spark above about 7000 rpm but won't work without a box.

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Thanks for the insight, and perhaps you can help. I have the pertronix points conversion, and it is incapable of powering my factory tic toc tach. Apparently the tach is looking for "sine wave" and the pertronix uses "modified square wave". Their advice was "get a new tach", to which I replied "Why would I replace my factory tach when I can replace your $70 junk".

Anyhow, can you advise which unilite conversion (if any) will power the factory tach correctly? I had a GM product with unilite conversion and Hyfire IV that had no problems with an old SunTach.

Thanks, Eric

I am an engineer at Mallory/Erson.
That is a tough one. The output of the Unilite/MBI/E-Spark is also a square wave. Most tachs will still function when you install an electronic ignition but sometimes..........
Aftermarket tachs always work with aftermarket ignitions because the aftermarket tach company has no idea what kind of ignition you will be using so they design their tachs to work with almost any kind of signal. Stock tachs are designed to be made as cheaply as possible and often only work with the stock ignition. Sometimes the problem isn't the shape of the output wave form but rather the fact that points pull the wave all the way down to zero volts when they are closed where electronic kits only pull the voltage down to about 1.5 volts. In this case, it is possible to add a few diodes and resistors from Radio Shack to the wiring of your car and force the voltage to zero for the tach wire. This may or may not work but it is the only option you have if you want to use your stock tach and an aftermarket ignition.
Send me a private message with your mailing address and I will send a diagram showing you what diodes and resistors to buy and how to hook them up. If it works, post the info on this forum for others. If it doesn't, I am out of ideas.

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