I was just asked this question and didn't have an answer.Has anyone had the experience and what happened?

It will work, but the max output is lower, and looks funny on a scope.

Can't tell you how many times over the years I have seen them hooked up backwards. They run fine, but don't make max spark. I switch them to the correct positions and don't notice any difference. I assume that it does some damage to the coil from running it backwards, but don't really know for sure. I always put a Jacobs coil on everything eventually anyway.

I saw some backwards also.On the scope the pattern is reversed.Our scope also showed max output voltage.It pretty much showed the same as when hooked up correct.Kind of freaks you when you see the patterns upside down the first time.Never saw one that didnt run when it was wrong.Rocky

These replies are correct, it still works but shows an upside down pattern on the scope, if you still have one of those stone age machines. Any way the more important question is do electrons flow from positive to negative or is it really the reverse? There are a lot of thoughts on this but yet all the positive ground cars were electrical pieses of poo, but that could have just been because Lucas did the electrical on them. lol

It's like the old joke, Do you know why the British drink their beer warm? Because Lucas makes their refrigerators.

You old timers will get it, you young guns may not.

Just ran into this on a studebaker Im working on for my dad which is 6 volt pos ground When switching to neg ground it is recommended to reverse wires as it will cause accelerated point damage if not.

Car would start, but didn't run well...

It will reduce the life of the coil... the 2 different
windings also have different size wires and the thin
wires dont last all that long

Yep it gives a weaker spark. Dont you guys remember the old pencil trick in the older Motor Manuals to tell if the coil polarity is wrong ? Ron

?TAHW

It depends a lot on what the system is built like. Old points ignition systems had a capacitor that charged up as the points were open and when the points closed the capacitor (called condenser in those days) discharged through the coil, pulsing the coil primary inducing the current into the coil secondary causing the high voltage spark. If the points and capacitor w ere on the ground side of the coil, the inductance and resistance of the primary winding could be enough to keep the capacitor from charging up as high as if it were on the positive side of the coil. I have not looked at newer systems enough to guess if the same principle applies or not, but a coil is not a polarized device by itself, but supporting parts may be.
A car coil is actually a transformer, two separate windings, primary (low voltage in this case) and secondary (high voltage in this case). The transformer can be wired as a step up or step down, depending on the need.
If you tried to apply the low voltage into the high voltage secondary, then you would get very low voltage out of the coil primary and not have enough voltage to ever jump the gap on a plug. An older ignition system would have about 20,000 volts out of the coil secondary and if you pulsed the 12 VDC to the high voltage side of the coil, the output on the low voltage side would be very low, in the .0075 VDC range.

Danny

On most older coils the + primary terminal connects to both the primary and secondary windings. The primary windings are on the outside of the secondary windings and the primary windings go from the + terminal to the - terminal. The secondary windings inside of the primary windings go from the + terminal to the center coil wire hole. So when the primary windings circuit is opened the collasping induced magnetic voltage cuts thru the secondary windings and makes a very large high voltage spark in the secondary winding coming out of the coil terminal. So if hooked up backwards the voltage to the secondary winding would have to backtrack thru the primary windings to the + terminal and then thru the secondary windings. So the voltage to the secondary windings would be reduced by the resistance of the primary windings since it would go thru the primary windings and then the secondary windings causing lower voltage and amperage output. It would still run but as was stated will have a lower output and could cause many problems. The condenser just charges while the points are closed and helps the primary windings to colaspe as it keeps the point current from trying to arch and then helps induce voltage in the windings. Ron

Lucas the Prince of Darkness.I had a buddy that had a Triumph 650.I think every week we worked on the electrics.Guy I went to school with has a Triumph 650 now.Its the only one Ive seen that the electrics work on.Rocky

OK so what's the pencil trick?

Bought a used 69 Dodge in 1976 with a big block and totally stock, points style ignition.
Car would start fine and ran fine until the temperature got down to about freezing, then it would not start if left to get down to ambient air temp. If put in the garage to warm up, it would start with the starter motor, otherwise you had to push it to start. (4-sd.)
After dealing with this for 2-3 months, started looking at everything and decided to replace the coil thinking it was "weak".
Found the previous owner had a kill switch wired to the coil and the leads were re-installed on the coil backwards. Switched them back and everything was fine.
By the way,it only had 8,300 miles on it, I still have it ,it has 27,000 on it now, and the original coil is still in it.
Most puzzling thing I ever saw.
The original owner never had a problem because He only drove it on nice summer days. I knew the car since new, bought it from my cousin, the original owner.

Jay