I knew a fella that hooked up his battery backwards and was burning out points until some one pointed it out to him? At least that's what he told me.
that's pretty much 100% BS too. There's some other part of the story thay are not telling you.
apparrently there is some huge lack of understanding of basic electronic concepts AND how a kettering ignition system ACTUALLY works.
at the root, you have a battery, a coil with a primary and a secondary, and breaker points, and a condensor.
power from bat thru coil and closed breakers . IE.. primary current flow. mag field charges, breakers open, mag field collapses, induces a voltage on the secondary which is the high voltage discharge. Breakers are still opening and close enough to arc, so the condensor acts as a switch debouncer for a few moments untill the point gap widens. rinse and repeat.
too small a points gap and they never open enough and will arc and burn.
open condensor and the points will arc and burn
shorted condensor and the points will never actually open, as the condensor is across the contacts, and that just leaves you with current flowing in the primary circuit... leading to eventual thermal damage of the coil, dead battery, and non running engine.
oil/grease ont he breaker contacts will cause arcing and burning
too much primary current ( 6v coil in a 12v system ) will lead to reduced points life due to thermal damage and excessive metal transfer and pitting of the breaker contacts.
too little primary current ( 12v coil in a 6 v system, or a 12v coil in a 12v system PLUS some ballast resistor added in because the users doesn't know electronics ) yeilds no spark, or very weak spark.
Lastly, ultimate voltage of the spark at time of arc is defined by the size of the arc gap, and the physical characteristics of the atmosphere of the cylinder in which it is firing. In other words.. if doesn't matter whether you buy a stock coil or one of the fancy ones that claims 80,000v... the spark will still jump at say.. 9000v, if the arc gap and physical atmospher of the cyl allow it to do so... thus using stock plugs and gaps, you NEVER see the inflated claims made by some components.
It pays to actually know a little bit about this stuff.
As for the backwards battery / reversed polarity. it makes a LITTLE difference. the biggest difference can be measured ONLY with an electron microscope, and a very expensive, very sensitive piece of industrial grade equipment.
The issues? metal transfer direction of the breaker contacts. SOME contacts are set for a polarity, and have different coatings on each of the breaker contacts. .. Mostly these days, they are ALL the same, both sides.. so this part makes little difference. ( you might have seen this in some mechanical voltage regulators that ware also marked with a polarity preference ).
secondly, you can get a big resistance vs a big resistance plus a little resistance issue on the coil if ran at incorrect polarity.
take a typical 6v coil that needs no ballast resistor. primary impedance ( kinds like dc resistance ) can be around 1.5-1.8 ohms. the secondary may be 4000-8000 ohms.
If you have a polarity mismatch on some coils, you may be seeing a 4000+1.5 vs 4000.. IE.. not much difference. some applications this is difficult to correct.. like the ford 9n/2n/early 8n front mount coil.
Notcie the voltage and impedance relationships. your target primary current is usually somewhere around 4 amps a little more or a little less, depending... usually less.
when you see a ford front mount coil/tractor that is 6v, it also uses a ballast resistor. but when you see a ford 6v coil / side mount.. it does not use a ballast resistor.. why? coil impedance. the front mount is not a 1.5-1.8 ohm coil. it is a .9-1.2 ohm coil.. thus it needs a ballast resistor inline with it to maintain a correct primary impedance and thus primary current. without it, primary current would be 5-6 amps or more. the side mount coil already has the 1.5-1.8 primary it needs due to the way the coil was designed.. the correct number of turns of the correct sized wire. Move up to the 12v fords in the 65+ range... they used a resistor wire, and a 6v coil, and a bypass relay. Relay put full voltage to the coil when starting, because full voltage won't be 12v when starting due to increased starter demand from the larger engines, and the still anemic battery technology of the day., once started, the resistor was no longer bypassed, and thus you have a 6v coil, plus resistor, running on 12v. primary impedance and primary current were both happy.
That's the basics of the why and how of it.
