To further clear up what I believe to be INCORRECT information posted below, here's what one person in quotes has posted and my engineers response. My analysis is based on my electrical engineering education (BSEE Purdue University), and over 40 years of experience in electronics and being an old tractor dealer having to repair the darn old things lol.
A person is entitled to their own opinions BUT NOT THEIR OWN FACTS...
1) ?That to is a myth and as long as you have the correct coil or the correct ballast resister in place the point do not care which way current flows?
CORRECTION no points don't care what direction current flows HOWEVER the coil sure does, see the reasons why below in my post
2) ?Misconception that a coil wired backwards will cause problems.?
THAT IS COMPLETELY WRONG see the reasons below
3) ?Ya the spark maybe jumping backward but it will be very close to the same voltage?
THAT IS COMPLETELY WRONG If wired at the wrong polarity the voltage must rise perhaps a thousand volts or even a few thousand volts higher in order to arc jump current across the gap. A few years back a Nuclear Physicist wired the same plug to the same coil and measured voltages with correct versus incorrect polarity AND IT TOOK ALMOST FOUR THOUSAND VOLTS HIGHER VOLTAGE if the coil was wired wrong.
Here is the re posted engineering analysis I posted below. DO NOT believe me, research scientific literature from competent trained professionals and engineers and technicians and then form your own opinion of whether or not a coil should be wired at the correct polarity or not and the bad effects if its not.
A COPY OF MY POST BELOW
COIL POLARITY DOES INDEED MATTER AND MAKES A DIFFERENCE
Does anyone really believe coil manufacturers go to the trouble and time and expense of labeling coils with + and - terminals IF IT MADE NO DIFFERENCE HOW THEY WERE TO BE CONNECTED ???????????????
If it made no difference why have those + and - labels on them?????????????
Why have labels + and - but just have no label at all if it didn't matter how they are wired ??????
Without going over the heads of Billy Bob and Bubba, I will try to explain in simple terms the reasons I believe a coil is labeled + and - and why it DOES MAKE A DIFFERENCE AND WHY THEY BOTHER TO LABEL THEM + and -
Its easier to emit an electron from a hotter to a relatively cooler surface THATS WHY VACUUM TUBES USED A HEATER UNDER THE NEGATIVE CATHODE from where electrons were emitted up to the much cooler Positive Anode Plate. No reason for all the expense and construction and energy used to heat the Cathode if it didn't make any difference now is there???????????
Similar in a spark plug the ground strap is MUCH cooler then the hotter electrode tip exposed out there in the combustion chamber. On those its much easier to emit electrons from the hotter tip to the much cooler ground strap. If a coil is wired at the correct polarity as designed for and labeled by the design engineers, its also easier for the electrons to jump SAME AS IN A VACUUM TUBE WITH HEATER UNDER THE CATHODE. If its wired bass ackwards the plug still fires and indeed yes still has a spark BUT THERES LESS SPARK ENERGY (Amps x Volts X Time),,,,,,,,,,,The system is less efficient,,,,,,,,,,,And the coil runs a bit hotter as it has to work harder and climb to a higher voltage before its energy is released and dissipated. My nuclear physicist friend made a study of the firing voltage of a plug when the coil was wired correct versus if it was wired incorrect polarity, and the coil had to raise several thousand volts higher in order to fire the plug at the wrong polarity then if correct BECAUSE SAME AS IN A TUBE, ITS EASIER TO EMIT ELECTRONS FROM A HOTTER TO A COOLER SURFACE
IN ADDITION I was a farmer and used tractor dealer for yearssssssss and therefore owned and worked on more tractors then any 10 other typical farmers and have nearly 50 years of experience in tractors and old cars and electronics. I SAW AND LEARNED FROM EXPERIENCE THE EXACT SAME THING THAT COIL POLARITY MAKES A DIFFERENCE EVEN WITHOUT ANY ENGINEERING REASONS WHY.
Soooooooooooo if anyone can explain the theory it makes NO difference how a coil is wired and why the coil makers bother to place + and - labels if it doesn't matter, Im all ears, but it has to make sound engineering sense not old wife tales and urban legends lol Im never to old to learn so please explain to me why it don't matter how they are wired!!!!!!!!!!! And if so, why do the coil makers bother with those + and - labels in the first place
MY ADVICE WIRE A COIL AS ITS LABELED NOTTTTTTTTTTTTTTTT WHAT YOUR BROTHER IN LAW OR BILLY BOB OR BUBBA SAYS
However, its a free country and yall are free to wire them as you please regardless if its right or wrong. HOWEVER DONT BELIEVE ME, STUDY AND RESEARCH IT YOURSELF and listen to experts, NOT me or Billy Bob or your know it all brother in law lol See if you can find why a coil maker bothers to label the terminals + and -.
I MAY BE WRONG AS RAIN (wont be first or last time lol) AND IM WILLING TO LEARN SO HELP ME OUT HERE, BUT IM PRETTY SURE COIL POLARITY DOES INDEED MATTER...
John T BSEE, JD Electrical Engineer retired Yall keep safe and heres an early Merry CHRISTmas I hope this helps