6 replies to this topic

[igor253]

Hi,

I am not very good with electricity, I have a used Lucas coil, and I need to connect it. I have two labels on the coil "CB" and "SW" where do I connect the distributer?

Thanks in advance!

[Cooperman]

Hi,

I am not very good with electricity, I have a used Lucas coil, and I need to connect it. I have two labels on the coil "CB" and "SW" where do I connect the distributer?

Thanks in advance!

SW is 'Switch' which is the input from the ignition switch.
CB is 'Contact Breaker' (i.e. distributor points or electronic equivalent) which is the output to the low-tension side of the distributor.

[dklawson]

SW is 'Switch' which is the input from the ignition switch.
CB is 'Contact Breaker' (i.e. distributor points or electronic equivalent) which is the output to the low-tension side of the distributor.

That is/was true. HOWEVER, the only coils I have ever seen with CB and SW markings were old... as in from the days of "positive earth". Did they keep using those markings for negative earth cars/coils?

When OLD coils with those markings are used on negative earth cars (not sure when BMC/BL changed) the CB and SW contact usage is reversed (CB to the ignition switch, and SW to the distributor).

[Deev]

Well I bet that's clarified things for the OP...

[dklawson]

Yeh... I'm sure it did. Keep in mind that the coil will work hooked up either way, however, wired "backwards" the coil will produce less energy. That's why the terminals were marked in the first place.

However, let's bring up another coil related point that really is worth mentioning.

The benefit (potential benefit) of a performance coil is a hotter spark through higher voltage. However, you will NOT improve the heat of the spark unless you open up the spark plug gap. It is the plug gap and the behavior of the fuel/air mix that controls the spark voltage, not the coil. When you open the plug gap up you can develop hotter sparks but only because the voltage must be higher to jump the plug gap. Here is the rub. With a points ignition system, you cannot open the plug gap up (much) because the switching of the points superimposes mechanical limitations on the charge/discharge of the coil. If you have an electronic ignition however, you can take advantage of its switching characteristics and open the plug gap up.

So in conclusion, a Sports Coil is good only for bling unless you have electronic ignition. Others will have to comment on whether modern sports coils use the SW and CB markings. I would be surprised if they do. Hooked up backwards, the coil will still work but at reduced power... which defeats the purpose of installing it in the first place.

[Cooperman]

Yes, I must admit that I can't remember when I last saw a dizzy with SW and CB markings. It seems to be +ve and -ve now, which is easy to understand.

[bmcecosse]

Well answered DKL! So - to get back to Igor - if the car is negative earth, and most Minis are, the CB should be connected to the power cable and the SW connected to the dizzy - normally a white wire with black stripe. There is however a further complication........these old CB/SW coils are rated for 12 volts, but Minis from ~ 198? have used a ballast ignition system, with a 9 volt coil. So - if yours has ballast ignition, a 12 volt coil will give a seriously weak spark........ Why are you changing the coil in the first instance???