Techtip10

SAVVA - Technical Tip 10

Getting a Positive Spark

Many of us have fitted a replacement coil to our early cars,
or the previous owner has. The question is, are they correctly connected?
A coil will work whichever way you attach the low voltage wires to it, whether it’s 6 or 12 volts.
It will however work far more efficiently if it’s correctly wired.

Most modern coils have their terminals marked + and –, or in some cases, SW
(for ignition switch) and CB for (contact breaker). Both are self-explanatory.
The important thing is to make sure they are correctly connected. If they are not
correctly connected the efficiency of the coils high-tension output will be severely impaired.
Electricity flows from negative to positive and not the other way around as most people think.
If the negative electrode is at a higher temperature than the positive electrode (as it would tend to be),
electron movement is easier and you get a healthier spark for any given high-tension voltage on the coil.

Many earlier cars (mainly British) have been changed from positive earth systems to the
more modern acceptable system of negative earth. Obviously, when making the change over,
the polarity of the petrol gauge and ammeter will have been changed around to make them operate
correctly. Unfortunately, so often, the coil connections have inevitably been overlooked.
Make sure they have also been changed over.

Last but not least, many a collector has replaced an old coil with a bright and shiny one
from a scrap yard not realising the replacement coil requires a resistor in line with the positive
connection (this applies to 12 volt coils only). Without going into the ramifications of this system,
the bottom line is that you are putting 12 volts on a +/- 8-volt coil – the result will be a burnt out coil.

(Eric McQuillian)