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I put an alternator onto a 239 and went from positive to negative ground and went to 12 volt, do I have to turn the coil around because of this? I now have the positive side of the coil going to the distributor, is this correct for a negative ground?
I put an alternator onto a 239 and went from positive to negative ground and went to 12 volt, do I have to turn the coil around because of this? I now have the positive side of the coil going to the distributor, is this correct for a negative ground?
They should be switched. Positive to the ignition switch, negative to the points/distributor.
I have heard advice both ways from several sources. If you look at the internal construction of a coil, switching the primary wires means the secondary winding is getting battery power only after it passes thru the primary winding, reduced quite a bit. (The picture is of a 12v neg. ground coil)
A better bet is to buy a 12v (-) ground coil, either with internal ballast resistor or with an external ballast.
Proper coil polarity has absolutely nothing to do with positive or negative ground. Sounds strange, but it's true.
Incorrect coil polarity reduces spark output at the plugs by about 25%, the engine will run when connected either way, but it may misfire under heavy load.
So are you agreeing with me, that the wires should not be swapped? I can't tell. That 25% sounds a lot like the reduced voltage to the secondary windings.
So are you agreeing with me, that the wires should not be swapped? I can't tell. That 25% sounds a lot like the reduced voltage to the secondary windings.
The coil is just a transformer, it will work either way. The spark plug cares though, has to do with the energy required to initiate a spark. As electrons "like" to jump from the hot center electrode to the relatively cool ground strap. The problem is who knows how some of the old coils are actually wired internally? It might say "Bat" and "Dist" instead of + or - ? Pos ground coil or?? So it's best to actually check.
There are a couple easy ways to test this. If it fails the test just swap the wires around without regard to the markings on the coil and good to go. Some ignition guys claim that with a magnetic iron core, if an ignition coil has been run a long time with incorrect polarity it will have a permanently reduced or attenuated output.
The first is called the "Pencil test" done by inserting a pencil lead into the spark and seeing which direction it flares. I've decided that looks like a great way for me to get shocked. A voltmeter - analog type with a needle - works quick and easy.
You can also check spark polarity using an analog (moving needle) volt meter. Hook up a voltmeter with the negative lead to the plug terminal and the positive lead to the block. Set the meter on the highest volt range. Crank the engine over (no need to start it), and you should see an upward swing of the voltmeter needle (don't be concerned with taking a reading). If the needle swings down off the scale, your coil is hooked up wrong. To correct it reverse coil primary leads. Do not worry about the coil markings, but make note of them for future reference.
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