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post #1 of 9 Old 06-16-2019, 05:10 PM Thread Starter
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switch to coil wire size

Howdy All:
I'd like to know everyone's thoughts on what gauge of wire to run from the on/off switch on a Farmall Super M, down to the coil.
The common wiring diagram that someone is sure to post shows a 16gauge wire connecting the two. I'm wondering if this is a big enough wire or if it's to small and not letting enough umph to get to the coil or if I should step it up to a 14 or even a 12 gauge wire?
Thanks in advance for your 2 cents.

Poppa Dave

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post #2 of 9 Old 06-16-2019, 05:19 PM
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Re: switch to coil wire size

I'd use 14 gauge...16 gauge is "enough" but a thicker wire will hurt nothing..

12 Gauge is a bit overkill and tougher to route and crimp terminals on..

An ignition coil shouldn't draw more than 5 amps max ...


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Old 06-17-2019, 01:13 AM
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post #3 of 9 Old 06-17-2019, 07:23 AM
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Re: switch to coil wire size

That wire is a ground and 14 ga. is sufficient
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post #4 of 9 Old 06-17-2019, 03:53 PM Thread Starter
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Re: switch to coil wire size

Actually Junky, it's the feed wire from the hot side of the Amp gauge. I guess that I forgot to mention that in my original post. The tractor in question has had a 12volt negative ground conversion done to it.

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post #5 of 9 Old 06-17-2019, 05:09 PM
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Re: switch to coil wire size

In that case Dave, a 14 ga. wire would certainly work fine. Was the 16 ga. showing signs of heating up? Or are you like most of us and like things to be heavy duty and trouble free? I pretty much feel the same way when working on my equipment. Always opting to improve where feasible.
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post #6 of 9 Old 06-23-2019, 07:07 PM
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Re: switch to coil wire size

Copper wire will handle more current than it is rated for, and the rating is for constant amperage so that the wire will not overheat with a constant flow of a particular amount of current. With a circuit that switches the current on and off like is done by the points and condenser, you can work on the average current over time rather than the peak in order to size a wire so that it won't overheat. If the wire isn't getting hot when the engine is running, then it is handling the amount of current that the circuit draws just fine, and using a wire rated for higher amperage will not increase the actual flow of the current. So if it is running fine and the wire is not getting hot, then I would consider it a waste of time and money to replace it with a wire rated for a higher current.

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post #7 of 9 Old 06-27-2019, 10:52 AM Thread Starter
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Re: switch to coil wire size

Junky.
The smaller 16 gauge wire seems to be handling the load fine with no heating up.
I put an hour on it pulling a 10 foot disc around the field to see what would happen. It didn't even feel warm, so I will probably leave it as it was already there. Should it start to give me an issue, it will be replaced with a length of 14 gauge.
Thanks for your input.

Dave N.
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Kimberly, Idaho
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post #8 of 9 Old 06-27-2019, 10:59 AM Thread Starter
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Re: switch to coil wire size

Nouveau Redneck;
I love it when someone with more automotive knowledge than I have gives an excellent answer. A average peak load. I would have never thought of looking at it that way and your 100% correct.
After I ran the tractor for about an hour the other evening, the only wire that was warm was the main 10 gauge coming off the alternator. While I was contemplating going to an 8 gauge wire to handle the load (ignition only, which didn't make sense), I discovered the nut holding the wire on to the alternator was loose. Tightening that up solved that problem.
Thank You for your input!!!

Dave N.
Rust N Dust Acres
Kimberly, Idaho
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post #9 of 9 Old 06-27-2019, 11:01 AM Thread Starter
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Re: switch to coil wire size

Now on to other issues with the big red machine. Wiring up the headlights through the original style 12 volt switch, changing out the gear oil in the rear end and contemplating the installation of a 3-point hitch.

Dave N.
Rust N Dust Acres
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