The Ford Barn

Eighty · 07-04-2022, 11:13 AM

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?

Gary WA · 07-04-2022, 11:20 AM

That's the design of the coil power to both sides key on or off.

Big hammer · 07-04-2022, 11:29 AM

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!

Mulletwagon · 07-04-2022, 01:53 PM

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.

MAG · 07-04-2022, 02:01 PM

Points OPEN - voltage both poles on coil.

Points Closed - voltage on Battery side of coil
No voltage on Point side of coil.

Tom Endy · 07-04-2022, 02:59 PM

Sponsored Links (Register now to hide all advertisements)

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

nkaminar · 07-04-2022, 04:55 PM

This site is a good reference for all things electrical:
https://www.mafca.com/downloads/Semi...ex%20Janke.pdf

burner31 · 07-04-2022, 05:14 PM

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

07-04-2022, 11:13 AM	#1
Eighty Member Join Date: May 2010 Location: Central Michigan Posts: 40	Coil 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?

07-04-2022, 11:20 AM	#2
Gary WA Senior Member Join Date: May 2010 Location: Clinton,WA/Whidbey Island Posts: 4,457	Re: Coil That's the design of the coil power to both sides key on or off. __________________ www.whidbeymodelaclub.com

07-04-2022, 11:29 AM	#3
Big hammer Senior Member Join Date: Jun 2014 Location: Land of Lincoln Posts: 3,431	Re: Coil 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! __________________ Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done

07-04-2022, 01:53 PM	#4
Mulletwagon Senior Member Join Date: Jan 2019 Location: Florida Panhandle Posts: 626	Re: Coil 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.

07-04-2022, 02:01 PM	#5
MAG Senior Member Join Date: May 2010 Location: Austin, Texas Posts: 926	Re: Coil Points OPEN - voltage both poles on coil. Points Closed - voltage on Battery side of coil No voltage on Point side of coil. __________________ I noticed the harder I work the luckier I get!

07-04-2022, 02:59 PM	#6
Tom Endy Senior Member Join Date: May 2010 Location: Southern California Posts: 3,168	Re: Coil Sponsored Links (Register now to hide all advertisements) 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

07-04-2022, 04:55 PM	#7
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 5,873	Re: Coil This site is a good reference for all things electrical: https://www.mafca.com/downloads/Semi...ex%20Janke.pdf __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

07-04-2022, 05:14 PM	#8
burner31 Senior Member Join Date: Dec 2014 Location: Shawnee, Ok Posts: 3,479	Re: Coil Question, have you done anything to the system prior to this problem? ie: pulling distributor, pulling/cleaning wires...etc...etc __________________ Keith Shawnee OK '31 SW 160-B