Funny this topic has come up. I literally was working on an article about this on Sunday. I see this question a lot on Mini message boards so I decided to write everything down "once".
I am also not familiar with Mallory ignitions so I will present my answer as more generic.
If your distributor uses points there are two main types of ignitions used, standard and ballast. (There are some older aftermarket kits that use points to trigger electronics but I will not discuss them here). If your car has ballast wiring, you need to use a ballast coil. If you have wiring for a standard coil, you use a standard coil.
If you fit a standard (3 Ohm) coil to ballast wiring the coil will not develop full power and you will have weak sparks at the plugs. If you fit a ballast coil to standard wiring, too much current flows resulting in overheated components with significantly shortened life.
Lucas used two different schemes for ballast ignitions. One used a white/pink resisitive wire inside the wiring harness for its ballast resistor. The second (and smarter) scheme used an external, inline, ceramic/wire-wound ballast resistor (often piggy-backed onto the coil mounting bracket).
How do you know what you have? You make voltage and resistance measurements with a multimeter.
Remove the dizzy cap and put a coin between the points so they appear closed.
Turn the ignition switch to the run position.
Measure the voltage between coil (+) and ground, then write it down. Coil (+) is the terminal that does NOT have a wire going to the distributor.
Remove the coin you placed between the points.
Turn the ignition off and mark the low tension wires on the coil, then remove them.
Set your meter to measure resistance and measure across the coil's low tension terminals.
If you measured approximately 12V in the first test you have standard wiring and you need to use a coil with a nominal resistance of 3 Ohms.
If you measured 6V to 9V your car has ballast wiring and you need a coil with 1 Ohm to 2 Ohms of resistance.
Compare that information to the coil resistances you measured to make sure you have the correct parts.
You mentioned a Bosch coil. I am a very strong supporter of the Bosch Blue. It is an epoxy filled standard coil with a nominal resistance of about 3.8 Ohms. It is a good choice for use with standard and aftermarket electronic ignitions.
With electronic ignitions there are many possibilities. Let's focus on only two general categories, OEM Lucas, and aftermarket in general. Lucas OEM electronic ignitions typically need a special OEM coil (originally Lucas GCL143). That is neither a standard or ballast coil, it is unique to Lucas electronic ignitions and has a rating around 0.8 Ohms.
Aftermarket electronic ignitions fall into many categories. There is a lot of misinformation about how they are wired. The simple truth is that in virtually all cases, the ignition module can work with either a standard coil and its wiring OR ballast wiring and its coil. What is universally true is that for the ignition module to work properly the module must get power from a full, switched 12V source.
Most aftermarket electronic ignitions (Crane/Alison being a bit different) for negative ground will have two wires, red and black. The black wire goes to the coil (-) terminal. The red wire is power in to supply the module. On a standard ignition system that red wire is typically connected to coil (+) since coil (+) is at 12V. On ballast ignition systems coil (+) has somewhere between 6V and 9V so that is not a suitable connection point. Instead, the red wire is connected to a switched 12V location such as a switch connection on the fuse box. The important thing here is to make sure the module is powered by a full 12V.
Crane/Alison units typically have more wires and I believe their wiring colors are different. The basics remain the same. The coil (-) connection from the Crane unit is wired as the factory says. The Crane amplifier power connection would be to a switched 12V supply... just like the standard ignition.
Your original question was about removing the ballast resistor. If you have a Bosch Blue, it will be a "standard" coil and you would NOT use it with the ballast resistor. You can remove the resistor or run a 16 AWG wire in parallel to it... effectively bridging the ballast resistor terminals end to end. If you want to run an original ballast coil instead, that is fine also but you would need to retain the ballast resistor matched to it so the current is not excessive.
I am sure that is as clear as mud. The bottom line is that you need to match your coil type to the wiring type in your car. If you are fitting an aftermarket electronic ignition you need to make sure that the amplifier module gets full 12V power to operate correctly regardless of the coil type you decide to use.
Sorry for the lengthy reply. The reason I started the document I mentioned is so I can post a link to that summary document and NOT fill up a board post with a long message like this.
Doug L.
--Previous Message--
: Can't give you a direct answer, I don't
: use mallory ignitions, not that there
: is anything wrong with them.
: It probably uses an internally
: ballasted coil, you could do a google
: search on your coil to see if it is or
: not.
: Glen
:
: --Previous Message--
: Hi again.
: I have another issue now. Still
: getting ready to fire up this thing and
: am finishing up the wiring and plumbing
: and I've run into the ballast resistor
: and locating it. And more than anything
: else, is it necessary?? I have a
: mallory electronic ignition with a
: Bosch coil and I've heard that with
: electronic ign. you don't need a
: resistor. Is this true or just a
: "great idea"?
: Thanks P.J.
:
:
:
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