http://mgaguru.com/mgtech/ignition/ig108.htm
I thought that this was a particularly clear and cogent explanation of the coil. points and capacitor. You need a good capacitor! (aka condenser) ; on our cars the second set of points closes early, increasing dwell, so spark is better at high RPM .The MGA has only one set, OK for 4 cylinders for sure.
The longer the dwell, measured in time, the more energy stored in the coil=hotter sparks. The little jumper wire in our distributor from the input nut to the point set is I think factory insulated with some kind of loose cloth sleeve that falls off. Taping it is a big no no as the plate all this is on moves rotationally with vacuum advance, flexing that wire, , and that will break off the small wire at the end of the tape ball! Normally the untraflexible wire is in a U shape and free to bend on its whole length. Further ,tucking the wire down against the distributor body on its way to the terminal if taped probably jams the vacuum advance up, too. MPG will drop. .There is a comapny called Olflex that makes ultra flexible wires. We should repro that wire in better stuff and get rid of that crazy pile of mismatched odd design terminals on the screw, too. Must have been an ME doing EE. A longer hex head screw helps.
Why i write this, is both J-Y's car and Noel's had the ball of tape on the litle wire jammed down in that space ; shows whoever did that does not understand that it has to move ----cannot be taped up. ...
Will look onto olflex wire. This failure mode or grounding out of that wire happens to LOTS of 300's...