electrical question

[Deny1950]

started doing some wiring and was wondering how to connect the coil wires. The coil has a plus and minus on it and i am running a 6 volt positive ground. So my question is do i run the positive ground to the negative side of coil ? also would any one know what kind of flasher should i get for positive ground 6 volts flasher for led lights? Thanks Denis

[alexiskai]

The car will run either way, but in general the way to do this is:

1. Take your best guess at how it should hook up
2. Run a coil polarity test
3. Reverse the leads if the test shows it’s hooked up backwards

[Jim/GA]

Originally Posted by Deny1950

started doing some wiring and was wondering how to connect the coil wires. The coil has a plus and minus on it and i am running a 6 volt positive ground. So my question is do i run the positive ground to the negative side of coil ? <snip> Thanks Denis

Denis-
The short answer to your question is that the wire that you connect to the + post of the coil needs to find its way to the points inside the distributor (because your battery is hooked up positive ground).

This wire going from the coil to the distributor can also have a key switch in it, if you want. This is how Henry wired up the Model A originally. So the - post of the coil gets power run to it from one of the posts inside the terminal box on the firewall.

As an alternate approach:
Some guys like to make the key switch turn the power to the coil on and off, so the switch goes between the terminal box and the - post of the coil. If you do that, then the wire coming off of the + post of the coil goes straight down to the distributor.

I hope this helps.

[Tom Endy]

Bratton's sell a little device you plug into the top of the distributor that has LED lights that indicate coil polarity. I bought one many years ago and took it along on a club tour. We tested about 20 cars and found and about half had the polarity reversed.

Part number 17140 $25.00

Tom Endy

[nkaminar]

Just use your voltmeter. With car running, measure the voltage at the coil connections. If backwards, reverse the connections.

[CT Jack]

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Follow Jim/GA instructions. When the points close they complete the circuit to ground (+). This is the correct connection for a positive ground system. Keep it simple.

[rotorwrench]

The coils Ford used from the model A era to well after the war were marked differently than modern coils of the 12-volt era. Many has DIS on one side and BAT on the other. For model A coils I'm not as sure. Several manufacturers made them for Ford and there may have been differences. The best way to start was previously mentioned. Connect the + side to the ground breaker in the distributor whether it's an Electro Lock or not. The negative side either connects to the battery or the switch if it has one. It's all opposite if the car is negative ground polarity. With my distrust of modern things, I use the Nu Rex polarity test device to insure polarity.

[Tom Endy]

Many years ago, in my youth, my 9th grade auto shop teacher demonstrated to the class how to determine if you have the coil primary wires correctly connected so that the polarity of the high voltage spark reaching the spark plug is correct. If I remember right you want the spark at the plug to jump from ground to the center electrode, not the opposite.

The way they determined that back in the day was to start the engine and pull a spark plug wire loose so that there is a spark stream. You then insert the tip of a wooden pencil into the spark stream and observe which side of the pencil tip the spark flared. I forget which is correct, but what I remember is that Mr. White then handed the pencil to the class wise guy to have him try it. You have to be careful when you do this as you can get a pretty good shock.

The tool Bratton's sell is a lot safer and easier to use.

Tom Endy

[Rob Doe]

Originally Posted by nkaminar

Just use your voltmeter. With car running, measure the voltage at the coil connections. If backwards, reverse the connections.

Neil, if I read your post correctly:

If polarity is correct, if I test the voltage at the coil negative post, I should get a negative 6 volts and at the positive post a positive 6 volts. If polarity is reversed, the post and readings would be opposite???

There is another method that requires an old fashioned analog voltmeter set to its highest voltage i.e. 1000 volts on mine. With engine running, for a positive ground system, with the red lead on a good engine ground, for a split second (as quick as you can touch and remove) touch the black lead to the spark plug and watch which way the meter needle flicks.

It should flicker to the positive if polarity is correct???

Do not use a digital voltmeter for this test