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MG MGB Technical - Electronic Ignition, Coils and Ballast Resistors

Our car is a 1980 mgb roadster that we have owned for 14 years. A month ago I had Lumenition Optronic Ignition fitted, and although we only used it locally, all seemed well. Last week we visited some friends 60 miles away, and all was still well. On the return journey however, we went about quarter of a mile and the engine cut out. On attempting to restart, the engine fired and then died immediately. However, if the starter continued to be operated, the engine ran. I only did this for a few seconds! The AA was called. After investigation, the man said that he thought the ballast resistor had failed, and bypassed it as a “get you home” fix. The only thing strange thing was that the piece of wire that acted as the bypass had to be disconnected, as with the ignition turned off, the red light was still on – that is the coil was still receiving 12v (?).

On getting home I took it to my local friendly garage and left it there. He said that with electronic ignition you no longer need a ballast resistance, bypassed it and fitted a “standard” coil. Again, all seems well. The new coil is a Unipart GCL 333. The old one, a Lucas 102 High Energy 12v coil – on which it says, “use with a 1.3 – 1.8 ohm ballast resistance.

Now my questions!

Can anybody please explain in words of one syllable (or less!) what is going on? Has the electronic ignition caused the failure or is it just a coincidence? And more to the point is this “mod” to our precious car an OK one – that is that it will not cause any damage.

I’m sure you can tell that I am no expert, hence the request for a simple response.

Thank you.
E Davies

It was probably coincidence, the electronic ignition is unlikely to be taking enough current in excess of the original system to burn out the ballast, and permanently bypassing the ballast (a bit more sensibly this time) and using a 12v coil should cause no problems either. However the final decision must come from the makers of the electronic ignition system in either case.

Sounds like the AA jumpered from the brown to the coil instead of from the white/brown - not very clever if you needed to switch off the engine in a hurry.
Paul Hunt

This thread was discussed between 24/10/2002 and 25/10/2002

MG MGB Technical index

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