Coil

Eighty

Eighty

Member
Hey guys,question. Checking ignition. Car won’t start. When checking coil, with key off power to both side of coil. With key on, still have power to both side of coil. WHY?
 
With the points closed you shouldn’t have power, points open then you’ll have power. Clean the points if you have power no matter what!
 
That is a quirk of the Model A ignition system. On an unmodified sysem, the ignition switch is not located between the coil and battery like later systems. The switch is between the coil and the points. This is why both poles on the coil show voltage with switch off since the coil is wired directly to the battery. With the switch on, current flows from the coil through the switch to the points where the field is built and collapsed as the points open and close. With the switch on, there should be voltage on both sides of the coil when the points are open and zero when the points are closed.
 
Points OPEN - voltage both poles on coil.

Points Closed - voltage on Battery side of coil
No voltage on Point side of coil.
 
If you have voltage on both sides of the coil, turn on the ignition and put a business card between the points. If you don't have voltage at the arm of the points, the car is not going to start.

There is a whole shopping list of reasons why there is no voltage at the points, starting with the wire on one side of the coil, through the ignition switch, through the pop-out cable, through the lower plate in the distributor, and through the wire connecting the two plates together. Any number of places for the voltage to disappear.

Tom Endy
 
Question, have you done anything to the system prior to this problem?
ie: pulling distributor, pulling/cleaning wires...etc...etc
 
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