Background information on the Lumenition "Optronic Ignition" electronic ignition system.
Electronic ignition replaces the points (contact breakers) and the condenser in the ignition system. There are at least three different electronic ignition conversion systems out there that I know of; I chose the Lumenition system as I was told it was the most reliable system and the most suitable for a tuned engine with a sports coil. The contact breaker is replaced by a system which uses a four-bladed (four cylinders) "fan" connected to the existing distributor cam. The blades of the fan cut a beam of light which sends a signal to the control unit to permit it to cut and restore the power to the coil. In essence it is a very simple system.
I decided to replace the contact breaker system because I was tired of continually replacing the points - a horrible job on the Midget - as I was only getting around 1,000 miles per set (with the sports coil) before I the car started misfiring at high revs. Had it been a Morris Minor, where the points are nice and accessible, I probably wouldn't have bothered! A side benefit is, of course, far greater dwell accuracy and consistency, and the fact that the timing will no longer change as the points wear.

Cost
I paid £130 to a reseller. The system consists of two parts: the standard Lumenition system plus a part that is tailored to the distributor (in this case 25D4). The £130 includes both parts and VAT.

Prerequisites for installation
Because only a few components are actually replaced, it is important that the ignition system is in a good state of repair before the conversion is carried out. Otherwise it will probably be very disappointing as it won't help. The distributor bearings need to be right; the mechanical advance mechanism needs to work correctly. The coil needs to be in good condition, as do the leads and spark plugs.

Installation procedure
If the car is running well and is non-standard, you need to measure the existing timing so you can put it back correctly after installation, or at least know what the difference is.
Then you follow the instructions on the pamphlet, which consists basically of the following:
- Site the control box. I put mine on the inner wing.

- Unplug the lead that goes from the -ve on the coil to the distributor (white and black). This is no longer needed, so the leads can be plugged into each other (one end is a male Lucar connector and the other is female, so that helps!).
- Take a lead from the feed side of the ignition system on the fuse box. I used No. 5 on the fuse box and there was a spare male Lucar connector there. This goes to the red wire on the Lumenition system.
- Take off the distributor cap and rotor and remove the points, condenser and external connector. These are no longer needed, but you might want to keep them for posterity.

- Fit the optical sensor where the points were and then the fan over the distributor cam. Refit the rotor and feed the three wires from the optical sensor out of the connector hole using the black grommet clip supplied. Ensure there is enough movement in the wire to permit advance mechanisms to function but that there is not too much otherwise the blade may foul the wires.
- Connect the purple wire from the control box to the -ve on the coil.
- Connect the plug from the control box to the plug from the optical sensor in the distributor.
- Start the engine.
- Check the timing.
The whole job takes around 1 ½ hours (the first time). Then you need to tidy up the additional wires which probably takes another half hour.

Benefits
Manufacturers claim increased power and greater economy but I can't verify this one way or the other. What I can say is that the car starts much better and runs smoothly all the way up to the red line without misfiring.
But the most important thing of all is that I'll never have to change the points ever again!