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MG MGA - Electronic Ignition

I am thinking of fitting electronic ignition to my 1960 mga, can anyone recommend a positive earth unit?

I fitted a pertronix unit to my positive ground 1959 MGA a year ago and am quite satisfied with it so far.
Tom Heath

Hi have you got mech rev counter still on your car, if you have then this co. jolley engineering at can supply one that is like the magnetronic system but for pos. earth but won't work if you have elecronic rev counter

regards gordon
g c pugh

You can't go wrong with the Pertronix unit.

Ditto - Pertronix (Aldon, same thing in UK) works well.
B Mayo

Petronix is the whip. Highly recommended.
T McCarthy

Petronix works briliantly and very easy to fit
David Speak

David - I thought you were unwell!
Terry Drinkwater

Another vote of confidence for Pertronix from me. Just received a unit for my B ordered from Retro Rockets. You pay in $s but they ship from the UK, with current exchange rates you'll find it's half UK supplier prices. I paid 42.50 delivered for mine which arrived just two days after I ordered it.
Mike BGT

If you use a Pertronix ignition system how does it replicate the automatic vacuum advance on the Lucas distributer one of the benefits of which is fuel economy - or do you give up this vacility?
J H Cole

JH. The Petronix unit mounts to the points plate, just as the original points do. Thus, it has no effect on the functioning of the vacuum advance unit. It is simply an electronic points system. When it works, it works very well and helps to cover up some of the problems experienced when using points in a worn distributor. When it does not work, it significantly more difficult to trouble shoot, especially along side the road. Hence, it is common to keep either a points/condenser set in the on board tool box, or a spare points plate with points and condenser fitted, to swap out in case of failure.

The Lucas distributors, to keep working correctly, need the annual maintenance listed in the workshop manual. This is often over looked after fitting one of the electronic points replacement systems, causing problems with the mechanical advance system and more rapid wear of the distributor bushing.

Ideally, an electronic points replacement system should be installed on a freshly rebuilt distributor and a regular annual maintenance/inspection/lubrication performed.

Les Bengtson

Hi all just a note that none of these systems appear to work with the RVI postive earth rev counter

g c pugh


I'm also interested in converting my MGA '62 with positive earth.

Can anyone send/email me the wiring schematics on the conversion? Does the electronic conversion sits completely in the distributor or do you have exra external parts to be mounted to the MGA? Do you also need a new coil?


Marc Vernackt

Pertronics makes a module for positive earth that fits entirely inside the distributor. The only visible clue is an additional power wire between the coil and distributor. There are a few others that may work with positive earth. As far as I know, the only reason to install a positive earth electronic ignition module is because one is too lazy to convert the car to negative earth on the day of installation.

Members of the Positive Earth Society and concours enthusiasts are obligated by general laws of the universe to retain positive earth in their car. Concours enthusiasts are prohibited by the same laws from ever installing an electronic ignition module. Once you step into the other universe that allows installation of electronic ignition, you are no longer obligated to retain positive earth.

There are obviously a large number of people who have managed to get past the expense and inconvenience and pitfalls of installing electronic ignition and have convinced themselves it is a good idea (in spite of all evidence to the contrary). Apparently there are also more people still working through that process of denial and self-delusion. In spite of my aversion to this subject, I have posted a few articles on installation of some of the more common electronic ignition systems here:
See articles IG-203 through IG-206.

Starting from the basics, creating spark requires power input to the ignition coil, a series wired capacitor on the ground return for the coil, and a switch to periodically short across the capacitor to ground. Originally the contact points perform that switching function. See the simple ignition circuit here:
Most electronic ignition modules are simply replacing the contact points with an electronic switch. Some more exotic systems may also do some signal conditioning, but they still have to do the switching.

Electronic tachometers come in two basic "flavors", inductive sensing or voltage trigger. The most common electric tach used for the MGA comes from the 1965-1967 MGB. This uses an inductive pickup to sense current surge in the wire supplying power to the ignition coil. See here:
The other type senses an on/of voltage signal, usually picked up from the distributor side of the ignition coil. As long as the tachometer is connected directly to the ignition coil in the originally intended manner, it couldn't care less how the switching is done. As such, when properly connected any tachometer should work regardless of the type of electronic ignition system that may be installed.

The problem most often encountered is erroneously connecting the tach signal wire to the electronic ignition module where is will be sensing some signal from the module rather than signal from the coil as originally intended. Solution is to connect the tach sensor wire to the coil, not to the ignition module.

Some manufacturers of electronic ignition systems will supply a special "tach adapter" module. This is most often a neat device for transferring money from your pocket to theirs (usually not required). In the special case of the MSD electronic ignition module there are multiple sparks being generated, so the tach adapter is necessary to avoid confusing the tachometer.

If you are still having trouble making an electric tach work with any electronic ignition module, lean on the supplier of the ignition module for the necessary information. If the supplier cannot tell you how to make their special equipment work with your tachometer, don't buy it (or send it back).
Barney Gaylord

Thx for the detailed info

Marc Vernackt

Thanks Barney,

You have just saved me a few quid!

I am really happy with how my car runs with it's old fashioned mechanical points, but, reading all this enthusiasm for electronics, was beginning to wonder...

I shall keep my points file and feeler gauge in my pocket for a while longer. That reminds me, must go and check my gap...

Neil McGurk

Nice one Barney but you have forgot the fifteenth rule of concours.
We too want to use and enjoy our cars so please change the rules so we can use:

We want to use modified engines.
We want to use better finish paint.
We want to use non standard hardware that looks pretty.
We want to use better quality underseal so unlike the original cars that would last about 3 years ours will last longer.

and of course many many more confortable modifications. So electronic ignition is avery minor thing to them

But they enjoy it and argue amongst themselves and as we have said many times before it would not do for us all to be the same!
Bob (robert) yes Y8 is toast again :)

I'll pitch in with Barney, with one big BUT.

If running a "performance" engine, then an electronic ignition has some practical advantages. I use the pertronix linked to a J&S safeguard. The Safeguard is a VERY nifty bit of kit that advances and retards the timing in real time on each cylinder, using info received from a knock sensor mounted at the front of the engine block where a dipstick hole is provided for eg Magnette.

This prevents predetonation whle allowing the timing to be advanced to produce maximum power automatically (beats the hell out of doing it with a Laptop).

For a normal engine, there's no great advantage over points. I do carry a base plate with points and condensor, and I have had to use it when a Pertronix failed. If properly set up, the standard set up is absolutely fine.
dominic clancy

I never did get my refurbished original distributor to work properly with Aldon's rebadged Pertronix ignition. I reprofiled the mechanical advance to what I believe it should be (I think the rebuilder fitted the wrong advance). In the meantime my car has been purring along (see my Worried from Preston Thread) with a Metro dizzy.

Maybe this weekend I could give it another try.....!!! On the other hand, I'm inclined to listen to Barney and stay with points.

Steve Gyles


Please contact me off line. I would like to get your opinions on the value of the J&S Safeguard. Have been looking at it for some time.


58 MGA
Larry Hallanger

This thread was discussed between 14/06/2007 and 27/06/2007

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.