Morris Minor Owners Club

I have a +ve earth saloon.

the old coil was wired white and black to terminal marked CB and white to the SW terminal

The new coil is labled + and - do I connect it + to the contact breaker points or + to switch?

It works either way, but I have read that it works better one way round, can anyone explain why?

Hello Roger,

the coil's polarity is:- match the coil terminal to the battery earth, so in your case, battery earth = +, coil + goes to the distributor.

Alec

I see - because it earths through the CB.

Does anyone have an answer as to why it makes a difference which way round it goes?

Many years ago, I had a car put on a crypton tune machine. Because the coil was wired the wrong way round, the trace on the machine was upside down.

Hello Roger,

the polarity of the coil affects the spark at the plug gap. The hotter central electrode is better at emmiting electrons than the colder body.
So if the polarity is wrong the spark intensity is reduced (the coil voltage doesn't alter) because the electrons are flowing the wrong way and having to emmit from the colder body.
Anyone old enough to remember thermionic valves will know that they had heaters to assist electron flow, this is exactly the same reason.
By the way there is a check using a lead pencil point between the HT lead and earth, if the sparks feather out after the pencil to earth, the polarity is correct.

Alec