Good Day,

I can not determine the correct wiring for my 1973 FLH coil! I do not see a positive or negative marking on the top or bottom of the coil! Can anyone help?

Thanks,
Jolly Roger

 

Doesn't really matter, what fits best.

 

typically the source comes into the coil on the left side and the right goes to ign module or points.(looking into the plug towers)
while it is true, it will fire in both directions, a lot has to do with the type of coil used as the polarity will be reversed and some issues can arise under certain conditions.

 

On dual fire coils it really doesn't matter which is points or power.

 

DOES COIL POLARITY REALLY MATTER?



COIL POLARITY IS ONE OF THE MAJOR CAUSES IN HARD STARTING OR MISFIRING UNDER LOAD OR ON ACCELERATION WHERE THE MOST DEMAND FOR PLUG VOLTAGE IS NEEDED. THIS OCCURS WHEN THE PRIMARY CONNECTIONS TO THE COIL IS REVERSED. THE VOLTAGE AT THE PLUG TERMINALS NEED TO BE OF A NEGATIVE VALUE AND THIS IS AFFECTED BY THE PRIMARY CONNECTIONS.

IF THE POLARITY IS REVERSED, THE CURRENT DIRECTION IS REVERSED ALSO AND THE VOLTAGE TO THE PLUG TERMINALS WILL BE POSITIVE VALUE.

WHY DOES THIS MATTER YOU SAY?

IT WILL DIRECTLY AFFECT THE AMOUNT OF VOLTAGE NEEDED TO FIRE THE PLUGS BECAUSE IT IS MORE DIFFICULT TO JUMP THE GAP AT THE PLUG. THIS LOSS COULD EQUATE A 20 TO 45 % REDUCTION VOLTAGE/CURRENT SUPPLIED AT THE PLUG.

THIS PHENONAMON IS RELATED TO TWO THEORIES: THE ELECTRON THEORY AND THE THERMIONIC EMMISSION THEORY. THE FIRST STATING THAT ELECTRON FLOW IS FROM NEGATIVE TO POSITIVE AND THE SECOND STATING THAT IT IS EASIER FOR ELECTONS TO BE EMMITTED FROM A HOT SURFACE THAN A COLD SURFACE (ELECTRONIC TECH IN THE TUBE DAYS REMEMBER THE HEATERS THAT WERE INTERGAL TO THE TUBE IN ORDER FOR THEM TO WORK).

USING THE TWO THEORIES, ELECTRONS WILL LEAVE A NEGATIVELY CHARGED AND HOTTER SURFACE EASIER THAN IF REVERSED. WITH PROPER COIL POLARITY, THE CENTER TIP IS NEGATIVELY CHARGED AND IT RUNS WAY HOTTER THAN THE PLUG SHELL. SINCE IT IS EASIER TO JUMP THE GAP, THE IONIZATION OF THE FUEL CHARGE WILL OCCUR AT A LOWER VOLTAGE (EVEN LIGHTNING IONIZES THE PATH TO GROUND BEFORE THE ACTUAL STRIKE TAKE PLACE). THIS ALIGNING OF THE CHARGE PARTICLES ALLOWS THE SPARK TO PASS THROUGH THE HIGH RESISTANCE OF THE GASES IN THE CYLINDER.

IF THE POLARITY IS REVERSED, THE CENTER TIP BECOMES POSITIVE AND THE SPARK MUST COME FROM THE COOLER PLUG SHELL AND THIS COUNTERS BOTH OF THE ABOVE THEORIES AND AS WAS MENTIONED AT THE OUTSET, A GREAT LOSS OF IGNITION POWER WILL OCCUR.
coils can be wound and inter-connected diff as well as how the coil is attached to the machine.
the above holds water for standard induction coil not inter-connected. the older ign coils of that era fall into this grouping.

 

Why does it matter I say!! You need to find someone that knows what they are talking about.. Only time I have a thermionic emission problem is when I eat Mexican food. In that case polarity is always the same.

Look at the schematic for a dual fire coil.. It don't matter which primary wire is used for power and which for points. One plug will fire reversed polarity..

 

there are some electrical laws concerning current flow and polarity.
will they fire, sure, but there can be issues under certain conditions.
there are many coils and diff arrangements but on the older style coil current flow makes a diff.
this was a good discussion in another forum, perhaps i can transfer some info.
a case in point was back in the 70's, ford had some ign modules made in, you guessed it, china. well our US electrical color coding diffs from them so the modules were miss-wire and ford had fits with ign and short lived modules till they found out why. the polarity was switched. on a light loaded low demand engine, no issues but load her up, all heck broke loose.
some coils need a ground path and some don't, rice was one that used ign coils that operated with out such coupling to the engine.
i am assuming he is using stock coil for the era, the same as my 1974ch.
there is a simple test to see polarity of the ign spark.
some say things about spark with plugs out and direction of flow which is not correct due to ringing in the coil. a good oscilloscope image shows all.

 

So you're saying the stock coil on a 1974ch needed separate ground connection for the secondaries?

 

since he did not specify which coil he is using, we have to assume a stock era unit.
below is a jpeg of wave forms.


there is a wives tale of placing the two plugs together and firing the coil and then they say one plug fires forward and the other reverse. although it appears that way open air, that really isn't the case under chamber conditions. again the wave form show why it appears so. after the initial strike, all the energy is not dissipated and the collapsing electrical field induces energy back into the secondary and if high enough will ring back through the two plugs touching but the field is reversed.
depending upon how the coil is magnetically coupled, determines how a ground plane interacts or needed.

 

Not sure how a single fire coil polarity has anything to do with HDs.

Stock era (70s) HD coils were all dual fire. HDs with only one set of points are dual fire. The only ones I know that were single fire were something like 61-63 panheads. I owned one and have a buddy that still owns one. 74 Sportster with stock ignition has a dual fire coil. So does a 74 shovel.

There isn't a old wives tail about come coils firing plugs in reverse polarity. It's a fact. Look at the schematic for the single fire coil. Current is flowing in one direction when spark first occurs so one plug has to fire with one polarity and the other with the opposite.