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MG MGA - Coils, coils, coils...

Yes, this thread is all about COILS...
So this is my situation:
I have been going through coils more than I should. I would say I have been through maybe 3-4 coils over the past 5 years, and another today, maybe a 1 1/2 old. The car is mostly unmodified, running with the 1500cc. She still has a generator and the coil is still mounted to it. Its not the original type of coil, as I have gone with cobalt wires with a newer type cap (all plugin type, I drive this car a lot...). I guess I am wondering how the wires should be hooked up to the coil. I have always kept the same sequence; i.e. when I change the coil, I make sure the wires are hooked up the way they were. However, I suppose from day one I was never quite sure how they should be hooked up. Also, the car is still a positive ground so I'm wondering if maybe the wires are attached wrong. Positive to the distributor and negative in the harness going to the generator?? Or the other way around?? I will check how it's hokked up in the morning to verify. Also any info about "resistors and coils" might also help. Any help would be great :-)

C Burnham

check out the following link for the best information around:
Here is a short summary from Barney's webpage:

A final note about terminal markings: Later production ignition coils were marked "+" and "-" on the primary terminals, which makes hook up pretty much self-evident. The primary terminals of early coils for positive earth setup were marked "SW" for Switch, and "CB" for Contact Breaker". In the positive earth system the ignition switch supplies power from the Negative battery post, and the contact points ground the other side of the coil to the Positive battery post. Therefore "SW" = "-" and "CB" = "+". This bit of knowledge and logic can avoid confusion if you change your vehicle from positive earth to negative earth. In that case you reverse the coil wires, and the "CB" terminal connects to the positive Switch wire while the "SW" terminal gets grounded to negative through the Contact Breaker. If you're still confused, buy a new coil with the "+" and "-" markings.
Mike Parker

Hello Christine,

There was a lost of quality for replacement coil for few years. Buying it was often like gambling...

I found quality brand like mallory or Accel, very popular for Hot-Rods, a good choice.


Jean G.
Jean Guy Catford

The proper coil for the MGA has a 3-3.5 ohm primary resistance. It is designed for use with breaker points and no ballast resistor. Any coil with this primary resistannce should work. Others are sold for transistorized ignition that are in the 2-2.5 ohm range. They will draw more current and therefore burn the contact points in an MGA quicker. A coil for use in a ballast resistor ignition has a primary resistance of around 1.5 ohms. If you install this type of coil in a MGA with no other mods, you will overheat the contact points and turn the plastic rubbing block to mush in about 10 minutes. Don't ask how I know.

The MGA is a very low-tech engine and does not require High Energy coils. It is generally, a low revving engine and has only 4 spark plugs, Not much of a chore for a coil. A generic coil will work just fine. I have run for years on one found at the local Farm and Fleet farm store. The package said it was good for 12V VW's and a host of tractors. I even think it was marked "non-ballast".
Chuck Schaefer


I just replaced my coil with a pertronix. I couldn't be more pleased.

Highly recommended.

See Mike's post for confirmation of the orientation.

But to summarize. In a car that still has positive ground, the lead from the switch goes to negative post on the ignition coil then the lead from the distributor goes to the positive.

Good luck.
T McCarthy

Christine, its likely you should, but don't have a ballast resistor and are running low resistance coils. A quick ckeck with a multimeter... Wrong polarity will not cause overheating but too much current will.
Art Pearse

Some great posts especially from Chuck and Art as they say make sure you are using the correct coil, ie do not use a ballasted coil on the car also as pointed out by Art having the low power connections the wrong way round will NOT cause this problem.

Finally from my point of viewa coil can be damaged by poor HT leads (Wires as you refer to them) or bad spark plugs. If the coil energy can not find an easy path to earth via the dissy wires and plugs then it can easily "track" to earth via another unsatisfactory route.

I am just wondering what faults you have been experiencing with your coils that have failed?
Robert (Bob) Midget Turbo

When installing your coil make sure you are not over tigtening the clamp resulting in a dent in the side of the coil. This reduces internal clearence and can cause an early failure
J Heisenfeldt

There are a lot of great posts and I thank everyone.
Right now the newest coil has no ballast (it says it needs an external ballast). The leads are hooked up as follows, postive is going to the distributor and the negative is going into another harness, assuming the switch.

However what has been happening is after a while, the coil just quits. Generally I carry a spare and Im off again, and mind you it does usually go a year, sometimes more, sometimes less. I suppose its highly probable I have been using not very good coils. I have spent anywhere between $25 - $50 for coils, anything that will fit to get me home...

I recall replacing the plugs maybe two years ago, and the wires are new last year, as well as the contact points and cap.

I will hook up a meter to the new coil as soon as I can. The ohm resistance details are making me think that too could be a problem.
C Burnham


"Don't ask how I know".......Funny!

My brother once ask, as have others, how'd I learned to work on cars? I ask them how did they learn to walk? Ride a bike? No one I know popped out knowing how to do this stuff. We just don't know we can't so we try. Often, not correctly the first time out.
But we learn...most of the time. The great thing about this BBS is that we can be forwarned and, hopefully, learn for each others experience! Cheers!
Robert Maupin

"Right now the newest coil has no ballast (it says it needs an external ballast)."

If the coil says it needs an external ballast, then it is the wrong coil for an MGA and will burn out if used on an MGA with the standard wiring.

The ballast is not part of the coil. When they say ballasted coil, they really mean a coil designed for use with an external ballast. When they say unballasted coil, they really mean one that needs no external ballast.

A coil that needs an external ballast(ie ballasted coil) is really a 6 to 8 volt coil. If you run it continuously on 12 volts it will burn up. A car designed to use this coil will have a resistor(called the ballast) wired in series with the coil to reduce the voltage. This ballast resistor is switched out of the circuit when the starter is energized to give an extra jolt to the spark when starting. A standard MGA does not have this ballast resistor or the switching circuit, so if you use this coil it will see a continuous 12 volts and burn up.

A coil that needs no external ballast(ie unballasted coil) is really a 12 volt coil, so it will operate continuously on 12 volts without burning up. This is the one you need for an MGA.
Jeff Schultz

This I how I found my new coil after a few weeks of use! I agree with T, between the failure and constant problems with the points/condensers, I finally switched to the Petronix's as well. Not one problem since the switch. I have since put Petronix on my TR3 restoration as well!

WMR Bill

Sorry for not responding Christine but went away for the long weekend. Anyway as Jeff has pointed out if the coil you are using say for use with an external ballast then it is the WRONG coil for the MGA and will be contributing significantly to your problems.

You need to buy a simple 12 Volt non ballasted coil.
Robert (Bob) Midget Turbo

Robert, I learn a lot quicker and the education lasts a lot longer when I make the mistakes. Somehow the pain of a mistake lasts a long time. I think nature intended it that way. We learn early not to touch the stove. I find that when you do something and it works right the first time, I don't learn as much. I have learned a lot!

Oh yeah, we were talking about coils. It looks like the engine vibration by mounting on the generator got the better on WMR Bill's Intermotor coil. The extra space in ignition coils can be filled with dielectric oil, epoxy or nothing but air (nobody fills them with tar anymore). Air will let things shake around internally eventually working things loose, such as the end cap or internal wiring. Dielectric oil adds a bit of dampening to the motion and adds some insulating properties. Epoxy holds everything in place relatively permanently and is a pretty good insulator too. In addition, the epoxy filled coils will prevent the mounting clamp from crushing the case. Pertronics makes some coils filled with oil and others with epoxy.

Again, the right coil for the MGA is one that is around 3.4 ohm primary and is labeled for non-balast applications. A proper generic coil can run as low as 13 USD and give reliable service. The correctness of a particular coil is not relative to the list price.
Chuck Schaefer

My original coil lasted for 40 years. Then I had 2 replacement coils (from an MG parts stockist) in 18 months. Quality aint what it used to be!
P. Tilbury

I'll double check what it said when I get her back from the shop. I am thinking I might want to mount the coild in a different spot, away from the generator. Plus a future plan is to convert the generator to a altenator, which will probably force the coil mount somewhere else anyway. Didn't the later models move the coil to the fender?
C Burnham

Greetings all,

What is the advantage, if any, to running a Lucus "Sports Coil"? I recently purchased a coil off Ebay that was described to be for an MGA but having read this thread, I see it isn't as it has a ballast and is rated 1.3-1.5. Glad I saw this thread or I would have burnt up the system! Anyway, I'm running an HRG Crossflow head on my car, I say "running" but I haven't fired it up yet. Would there be any advantage installing the "Sports Coil"? Cheers!
Robert Maupin

OK, well I just ordered the following coil, to have in the boot for if/when this happens again:

Should be ok, right?
Anyway, I'm surprised at all the posting for this issue, I'm learning more than I expected about coils :-)
C Burnham

That will do nicely thank you Christine. That is the coil I fitted to my car when it became mobile again some 6 or 7 years ago and never been any problem. Because it is a high power coil I set my plug gaps to 32 thou and time my engine at 32 degrees without vac connected and at 4.5K RPM.

If I were you I would fit that coil now and hopefully relax with your other one in the boot/trunk.
Robert (Bob) Midget Turbo

Thanks Bob, I hope it does work out...Its reassuring to hear someones been using on so long. We'll see how it goes.
C Burnham


As mentioned by J Heisenfeldt, take care in mounting the Lucas Sport Coil. If you are mounting it on the generator, be sure that the coil, the mounting bracket (strap around the coil) and the "coil steady plate" (Moss #473-120) line up w/o putting any undue strain on the coil body. The body of the Lucas Sport Coil seems to be much thinner than that of the older models. In mounting my Sport Coil I tweaked the body enough that the coil leaked and I ended up stranded on the side of the freeway.

Moss replaced mine and the replacement sport coil had a taller mounting bracket to the point that it does not even touch the coil steady plate. In any case I am planning to move the coil off the generator using the 1600 coil mounting bracket.

jjb Backman

I too have had a problem with coil failure and additional, condenser failure
The first three coils were miss marked by the manufacturer and were actually designed for an external ballast. They failed in miutes and a few hours.
My last north american coil failed after about 20 hours of use. Jeff Schlemmer []provided this information when I asked for advice.]"However, your failure of several coils tells me that you may have an engine grounding issue. I always suggest having at least 2 if not 3 ground straps from the engine to tranny to the frame. Condenser failures also are common with a bad engine ground. The coils are a more coommon problem. Many are coming from the same Chinese manufacturer and live short lives. Getting a good epoxy coil is cheap insurance! make sure whatever coil you have, it has at least 3 Ohms internal ballast (measured between the LT terminals) or you'll continue to have problems!".
I have followed Jeff's advice.

I had exactly the same problem. I own an MGA 1500 fitted with a 1620cc tuned engine that used to eat coils! They would last from 1 month to 6 months then fail. I replaced points, condenser, LT leads, HT leads, distributor cap and rotor arm twice and still it did it. I then changed my ignition to a 123 ignition distributor (no points, no condensor) and guess what, it still happened. The solution is to move the coil from the dynamo. I used the bracket that fits onto the O/S engine mount as used on the 1600 MGA and moved the coil. I don't know whether it is heat or vibration that causes the problem but since moving it I have had no further problems. I can recommend the 123 system, it made a huge difference to performance. Coils I used were original Lucas and new stock Lucas from Moss.
Tim Dudley

I had 20 years of using an original coil mounted on the dynamo, and no problems. It packed up last year, and I have again mounted the coil on the dynamo. So far no problems again.
dominic clancy

So I installed the new Lucas coil, hooked up the positive lead to the distributor (positive ground) and the negative to the ignition, taking care to not over tighten things to much. I did this while camping in Vermont and she made it back fine with no issues. It's a 2 1/2 hour drive to Boston. I still think one of these days I will mount the coil to the 1600 location, but so far so good.

In relation to electronic ignitions I will say this; I had at one point, in an MGB, converted it to an electronic ignition, a Pertronix I recall. It broke down twice (In the course of a year, maybe two) and both times I did not have spare parts for the newer ignition and we were pretty well dead in the water. On the second occasion, I took the old points out of the boot and reinstalled them in the car. I was able to get home :-)
That was the last time I played with an electronic ignition system. Its easier for me to carry a new set of points and condenser than to keep a back up box (expensive) with me, and cheaper. And I know those work...Some have seemed to have good luck with those systems but I didn't for whatever reason...

btw, here is a picture of Willie, Cecilia (the MG) and me in the mountains this past weekend...


C Burnham

This thread was discussed between 21/05/2009 and 01/06/2009

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