The Ford Barn

Sparta · 03-16-2020, 06:34 PM

This maybe a dumb question...but which of these two wires is negative and which is positive for the ignition coil? I’m replacing my old coil and noticed that the wire which stems from a stud on firewall was on the positive and that the red wire which seems to go through firewall to gauge cluster was on negative? This doesn’t seem right, but the car has been running and driving with that wiring? That being said...it’s been running rough which I’ve been trying to diagnose. Let me know, thanks!

Sparta · 03-16-2020, 06:48 PM

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The Master Cylinder · 03-16-2020, 06:48 PM

Stock wiring/positive ground? Wire from junction box to - and Red wire from ignition switch +.

Sparta · 03-16-2020, 06:55 PM

Quote:

Originally Posted by The Master Cylinder

Stock wiring/positive ground? Wire from junction box to - and Red wire from ignition switch +.

okay, in that case i had it wired with opposite polarity. would it be possible for the car to run in that manner?

Patrick L. · 03-16-2020, 07:03 PM

It depends on the battery ground. The ignition system is grounded thru the points so the wire to the distributor is wired the same as the battery ground.

Yes, the car will run fine [ usually] with the points/coil wired 'backwards'.

Sparta · 03-16-2020, 07:10 PM

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okay. i should note, it was the previous owner who had it wired as such. Is it possible that the reverse polarity is whats causing the misfire/sluggish engine?

1930 coupe · 03-16-2020, 09:01 PM

There are hundreds of different coils and very few cars are wired alike, so it is almost impossible to tell for sure by just looking at it. order a polarity tester from one of the vendors then you will know.

SteveB31 · 03-16-2020, 10:01 PM

Always remember the points are to ground, so if positive ground car, as original, the red wire , which goes thru the key switch to the points is the ground. If 12v neg ground, the. The black wire goes to the switch to points

Bruce of MN · 03-17-2020, 06:05 AM

This may help: http://www.chicagolandmgclub.com/tec...neral/574.html

Patrick L. · 03-17-2020, 08:21 AM

The polarity tester like 1930 coupe showed is a good thing.

Patrick L. · 03-17-2020, 08:23 AM

Quote:

Originally Posted by Sparta

okay. i should note, it was the previous owner who had it wired as such. Is it possible that the reverse polarity is whats causing the misfire/sluggish engine?

I would doubt it. It is a possibility, but not likely. I would think something else may be the problem.

rotorwrench · 03-17-2020, 08:39 AM

A coil that is connected with the wrong polarity will not work at its max potential. Polarity is important. A pencil can be used to check polarity but the Nu-Rex tool in post 7 is easier to use with no possibility of shocking the operator.

The weakest point in the model A ignition system is the condenser. It won't work well at all if the condenser is bad.

03-16-2020, 06:34 PM	#1
Sparta Junior Member Join Date: Jul 2019 Posts: 29	Which wire is positive/negative for ignition coil? This maybe a dumb question...but which of these two wires is negative and which is positive for the ignition coil? I’m replacing my old coil and noticed that the wire which stems from a stud on firewall was on the positive and that the red wire which seems to go through firewall to gauge cluster was on negative? This doesn’t seem right, but the car has been running and driving with that wiring? That being said...it’s been running rough which I’ve been trying to diagnose. Let me know, thanks! __________________ 1931 Ford Model A Tudor Complete stock rebuild Disregarding the constabulary since 1931

03-16-2020, 06:48 PM	#2
Sparta Junior Member Join Date: Jul 2019 Posts: 29	Re: Which wire is positive/negative for ignition coil? ... Last edited by Sparta; 03-16-2020 at 06:57 PM. Reason: wrong photo

03-16-2020, 06:48 PM	#3
The Master Cylinder Senior Member Join Date: Aug 2012 Posts: 880	Re: Which wire is positive/negative for ignition coil? Stock wiring/positive ground? Wire from junction box to - and Red wire from ignition switch +. __________________ The Master Cylinder Enjoying life at the beach in SoCal...

03-16-2020, 07:03 PM	#5
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Which wire is positive/negative for ignition coil? It depends on the battery ground. The ignition system is grounded thru the points so the wire to the distributor is wired the same as the battery ground. Yes, the car will run fine [ usually] with the points/coil wired 'backwards'.

03-16-2020, 07:10 PM	#6
Sparta Junior Member Join Date: Jul 2019 Posts: 29	Re: Which wire is positive/negative for ignition coil? Sponsored Links (Register now to hide all advertisements) okay. i should note, it was the previous owner who had it wired as such. Is it possible that the reverse polarity is whats causing the misfire/sluggish engine? __________________ 1931 Ford Model A Tudor Complete stock rebuild Disregarding the constabulary since 1931

03-16-2020, 10:01 PM	#8
SteveB31 Senior Member Join Date: May 2010 Location: Englewood, Colorado Posts: 1,372	Re: Which wire is positive/negative for ignition coil? Always remember the points are to ground, so if positive ground car, as original, the red wire , which goes thru the key switch to the points is the ground. If 12v neg ground, the. The black wire goes to the switch to points

03-17-2020, 06:05 AM	#9
Bruce of MN Senior Member Join Date: May 2010 Location: VA Posts: 1,410	Re: Which wire is positive/negative for ignition coil? This may help: http://www.chicagolandmgclub.com/tec...neral/574.html

03-17-2020, 08:21 AM	#10
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Which wire is positive/negative for ignition coil? The polarity tester like 1930 coupe showed is a good thing.

03-17-2020, 08:39 AM	#12
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,432	Re: Which wire is positive/negative for ignition coil? A coil that is connected with the wrong polarity will not work at its max potential. Polarity is important. A pencil can be used to check polarity but the Nu-Rex tool in post 7 is easier to use with no possibility of shocking the operator. The weakest point in the model A ignition system is the condenser. It won't work well at all if the condenser is bad.