From time to time I hear the question "What kind of distributor does my car have?" Well, maybe this will help. Below are pictures of two of the most common dizzies that are found in our little cars.
In the photos above, the dizzy to the left is a 25D. It was used from the start of MGB production until the mid 1970's. The caps have varied a bit through the years. The early caps take the sparkplug wires in through the side, later caps have them coming in through the top. Also notice that there is not an external wire, just a male push on connector where the wire attaches from the ignition coil. There is also a half-round cut-out in the cap to clear this connector. The other feature of merit is the small knurled knob directly behind the vacuum advance unit. Rotating this knob adjusts the timing slightly, either advances or retards it for fine tuning.
The second distributor in the photos, the one on the right, is a 45D. This
dizzy is a common replacement for the 25D. Lot's of MG's are
running around with this dizzy. There are several variations of this
dizzy, two being electronic and pointless that were used on cars after
1974, and are considered by some to be inferior to the normal 45D dizzy