Washington, D.C. Centre
the Spark

Electronic Ignition For ALL

"By Jim Lunson, tech committee


Last time I covered the points system and how this switching makes the coil work. One of the biggest improvements in the distributor function since almost the invention of the engine is the use of electronic ignition modules to replace the old points setup. These systems came into the picture in the mid 1970's, long before the sophisticated computer systems we see today. They were basically an assembly of resistors, diodes, and compacators put together to accomplish the same function as the points had done for so many years. What they did was provide the same "on/off" function without any moving parts.

This electronic "points" ignition was necessitated by the ever tightening EPA emission requirements imposed on the car manufacturers during the 1970's. These new systems provided two advantages: first they would automatically adjust the time the points were open and closed to make the coil produce the absolute highest voltage possible, and secondly the timing would never vary out of adjustment. This meant the spark plugs would always function at their optimum potential, insuring the least emissions; and by maintaining this without changing; the car's emissions would never rise due to wear and tear on this element. As soon as these systems came out, there was a noticeable increase in performance and aftermarket manufacturers began offering replacement kits to upgrade cars with the old style points. This is where the MG systems came into play.

British Leyland came out with their electronic system in 1975 in California and 1977 everywhere else. Their system consisted of a ballast resistor to obtain a steady 6 volt power supply and a small metal box built onto the side of the distributor to house the electronic components and relay the switching back to the coil (distributor #45DE). The system worked very well, but as usual with British auto manufacturing, was not properly tested. It seems that since the distributor was very close to the engine block and the engines ran on the hot side, heat soon destroyed the components in the little box and the system failed. In 1980, MGs relocated the box to mount it between the coil and the fender which solved the problem (distributor #45DM). With the rapid failure of the 1975 to 1979 models, an aftermarket system was a necessity and soon on the market. Today, a conversion kit is available for every MG made. These systems are all similar, but with special brackets to make an exact fit inside the distributor where the points used to fit.

These systems work on one of two methods, either a rotating magnet attached to the distributor shaft with a sensor beside it to signal the switching as it moves past, or a flat disc on the distributor shaft with slots in it and a photo cell to shine a light through the slot as the disc rotates. Both systems work very well. These systems contain a component to mount inside the distributor and a small box mounted somewhere remotely in the engine compartment to contain the electronic switching equipment, plus various wires between the two elements, as well as back to the coil.

The advantages of these systems are as noted above: absolute highest voltage possible to the spark plugs providing maximum spark for easier starting, increased power, longer spark plug life, better spark plug wire performance and better coil lifespan. All this, as well as no moving parts to either wear out or need constant adjustment. Instant noticeable improvement will be felt in performance and reliability at every turn, even over a brand new points system perfectly adjusted. MG expert John Twist estimates they provide 2-3 additional horsepower instantly.

There are however, some downsides to these systems. First, when they fail, there is no warning or erosion of performance like a points system; they just quit when the electronics fail and the car stops running on the spot. Secondly, when it comes to maintaining originality in an old car such as the MG, there is now a huge flaw as a stray black box appears, mounted somewhere in the engine compartment with lots of additional wires coming out of it running to the coil and distributor. It is obvious something has been added that was not there in the original car.

Reliability: A good point system will last a couple of years provided it is kept in top adjustment. No one knows the lifespan of the electronic systems as they continue to last and last. My 1979 MGB was fitted with a Piranha brand (forerunner to the "Luminition" and "Crane" systems) sometime in the early 1980s when the original system failed. This was an early version appearing when the problems noted above started to occur. I replaced it in 2005 after several people told me that although it was a good system and still working as good as new, after over 20 years, I was probably living on borrowed time. Failures have been rare as these systems contain no moving parts and are sturdily built to last and last.

The problem is that each system is designed to fit a specific distributor where the old points were mounted and there is no "one size fits all". Being an all electronic assembly, there is no repair possible, only replace it. So if it does fail, a replacement for an MG distributor is hard to find except through the parts mail order companies. The only protection against failure is to carry a back up system for your specific distributor. This runs up the cost as they are not cheap ($100+ vs. $10 for a points set). Or just hope they last and last like mine has and not worry about it.

The other option is to carry a set of the old points along and be prepared to make the conversion back if there is ever a problem. This takes some doing as all the wiring has to be changed back, but will insure a backup in case of a failure. Personally, I carry an old distributor with the points already installed as an emergency kit. I think it is easier to swap distributors than redo the points system inside. This is in spite of the fact that the old system in my car lasted over 20 years without being touched.

Originality: In the last several years, "Pertronix" brand has come out with a system that fits entirely within the distributor (they now even make a whole distributor with the system mounted inside). From the outside, there is no difference in the original look of the car with the exception of one additional wire going into the distributor. For all practical purposes, this solves the appearance problem yet provides all the benefits. My only concern with this system is that it goes back to the problem with the original MG system: perhaps too close to the engine block and the potential for damage from heat. I have had this system on my car since 2005 without trouble, so I am pretty sure it is more durable than the original MG system, although it is only 5 years old at this point. My previous system had the black box mounted on the fender.

So the conversion is available for virtually every MG, the cost is higher than points and there is an additional wire to the distributor, but the performance improvement is good, all wear is eliminated, and the reliability seems to be good at this point. The conversion is available for every MG. The decision is yours.


Back to Technical Tips