At 09:48 AM 4/12/03 -0500, Bill Miller wrote:
>Just double checking myself.
>
>1966 MK2 1200cc
>POSITIVE ground
>
>Old coil is marked: "CB" and "SW"
>
>New NAPA coil is marked: "+" and "-"
>
>Which wire goes where?
The coil is an insulated device and won't care which way you hook it up for
polarity- it only works on collapsing magnetic fields so it'll work either
way- although some coils will have a diode inside to check on polarity.
Anyways, "CB" would have gone to the distributor and "SW" to the ignition
switch.
The new coil will want "+" to the distributor and "-" to the ignition switch.
On most cars with points (and negative ground), power flows from the
battery to the chassis/earth, then through the engine block to the
distributor body. From there it moves through and is chopped up inside the
distributor by the points with each pulse then sent to the coil. Once it
passes through the field windings of the coil the current flows through the
wiring to your ignition switch and then on back to the positive side of the
battery.
When your points are closed, the coil is charged and runs up a
voltage. It's modest, but nothing spectacular. When you break contact
with those points, the magnetic field at the coil then collapses fast and
that sudden change in potential is enough induce a high voltage, low
current through the secondary windings of the ignition coil. That's the
main terminal lead that goes back to your distibutor cap and then on to the
plugs.
On a positive ground car, current flows the opposite way from the battery
through the ignition switch to the coil, then to the distributor, engine,
chassis and eventually back to the battery.
One of the hardest things to get through my head when learning about
electronics was that electricity moved from negative to positive
terminals. All power went to the chassis and then back to the battery
'backwards' in essence of what I had always believed.
-Vegaman Dan
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