Which wire is positive/negative for ignition coil?

S

Sparta

Member
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!
 
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'.
 
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?
 
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.
 

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