6 volt +gnd coil replacement question, 4 to 3 wire

Hi all!

I have a "64 IH 140 (6v + ground) with a bad coil. I purchased a new universal 6 volt coil, however it has 3 leads, where my OEM has 4. I figure "-" is common on the new one. If that"s the case then I should wire "-" to the distributor and chassis ground, and wire the ignition switch to "+".
Just wanted someone to confirm this before I make sparks fly

Thanks in advance!

Brady

educate me. What kind of a coil has 4 terminals or 3 terminals? You probably mean voltage regulator.

The coil should be wired positive to the distributor (matches the battery ground polarity)
The negative should be connected to the Key.
The remaining wires concern me some. I would attach them as they were, but on the terminals as I described. Jim

Simple transformers (like an ignition coil) would have 4 leads (at least internally) ; 2 for the primary, 2 for the secondary. In a lot of transformers 1 lead of the primary is "common" with 1 lead on the secondary, which are both typically connected to ground, hence the modern 3 terminal coil. So, my current coil has 4 leads, a sparkplug type wire and a screw terminal going to the distributor, and a + and - on the primary side (screw terminal) which go to ground and the start switch, respectively.

At least that"s the way I understand it to be ;-)

Thanks for the reply.
I'm pretty sure the way I intend to hook this up is correct...I'm an electronics geek, but it hurts my brain trying to visualize a positive ground system. My concern is that technically I'll be hooking the primary side of the coil up backwards to battery polarity (ground to - and negative to +). Ugh, there goes that headache again.

Connect the (-) to the ignition feed from the switch. Connect the (+) to the distributor points/condenser. The remaining lead should be the secondary led to the distributor cap.

Was your old coil from a magneto? I don't belief I have ever seen a battery ignition coil with four separate leads.

Electrically you cannot connect the primary leads, one to the ignition switch, and the other to ground, and have it work.Since you are working with DC current rather than AC in order for the magnetic lines of force to change to induce voltage in the secondary winding the primary winding must be turned on and off. That is the job of the points which must be connected to the grounded side. With the switch on and the points closed the current will flow through the primary winding and build up the magnetic field in the coil. When the points open the current flow stops in the primary winding which causes the magnetic field to collapse. The collapsing magnetic field induces the current in the secondary winding which will jump the spark plug gap when the voltage gets high enough.

Got a photo of that interesting little gem?

I see so many get all CORNFUSED about Pos Ground, but stop n think for a moment !! As far as the battery and the load device (coil, lights etc) THERES NO DIFFERENCE.

IT DOESNT MATTER ELECTRICALLY (not withstanding alternators that MUST use the iron as the - battery connection as their case/frame is one of their conduction points) WHICH ONE OR THE OTHER BATTERY POST JUST HAPPENS TO BE TIED TO A HUGE HUNK OF RUSTY OLD IRON!!!!!!!!!!!!!!!

The iron is simply used as the current carrying conductor instead of having to run 2 wires everywhere, use the hunk of iron as the wire instead.

For example, if a coil is CORRECTLY wired to a tractor that happens to have the hunk of iron tied to the battery POS post (called Pos Ground) the coils - gets to the UNGROUNDED battery - post (via wire and ign switch),,,,,,,,,,and the coils other + post gets eventually connected to the batterys + post via the points when closed and distributors atatchment to frame (which is tied to + on battery) NOWWWWWWWWWWWWWW on a Neg ground tractor GUESS WHAT!!!!!!!!! The coils - gets to the battery - via closed points and distributor frame ground while the coils + gets tied to the ungrounded battery + via the ignition switch ITS THE SAME GUYS, THE COIL - TO BATTERY - AND COILS + TO BATTERY + REGARDLESS WHICH BATETRY POST IS TIED TO TEH HUGE HUNK OF IRON !!!!!!!!!!!!!!!!!!!!!!!

Get it?????????????????

John T

Positive and Negative ground are like right hand and left hand threads on a bolt. On the bolts the nuts turn in opposite directions. With Positive and Negative ground current flows through the circuit in opposite directions.

The battery and charging system polarity must match.

Some electrical devices (such as diodes, ammeters, charging systems, ignition coils) are polarity sensitive, meaning that they are designed so that current must flow through them in one direction. They can work with either ground polarity simply by connecting them with regard to proper current flow direction.

"Ground" is the zero voltage reference point of the circuit so ground itself is technically neither negative or positive. Negative or positive ground simply indicates which battery post is connected as the zero voltage reference

Starters, lights and switches do not care which polarity they operate.

You are not connecting your coil backwards to battery polarity, you are connecting it for proper current flow direction.

You mention being an electronics geek. Therefore I assume you have had some experience with negative voltages in electronic circuits. Guess What...........negative voltages are positive ground.

Before anyone else responds, let me apologize as my mental picture of the coil does not match reality. Thank you all for your comments and criticisms, and thank you for confirming what I suspected: I'm an idiot ;-)
yes, there are only three connections to the coil. What was screwing me up is the wiring diagram I have for it, which shows ground being connected to the lead for the start switch. This is obviously wrong since that would create a short to ground as soon as the start switch was activated. This fourth connection (to ground) does actually NOT exist on the current coil's wiring, so in short I'm going to replace the coil exactly as currently wired.

Again, my apologies for wasting everyone's time. Next time I'll ensure what I'm saying is actually correct. I'm now off to eat some humble pie with my coffee.

Brady

OK with the coffee, but wait on the humble pie. A web site, cngco dot com, referenced in other posts on this site has a diagram for Farmall 140.

In looking at it I see two things that would lead a person astray.

(1) The battery is shown negative ground, but the coil shows positive post to distributor. With negative ground, coil negative goes to distributor.

(2) The coil to distributor connection is poorly drawn. It shows wire from coil going to side of distributor, but the diagram does not show a feed through at the side of the distributor. The line goes to the circle representing distributor and has a ground symbol also connected to the circle. This would indicate that the coil connects to the grounded distributor case. Diagram needs a feed through indicator

Several other diagrams in that series are incorrect. F 240 gas diagram also has battery-coil polarity mismatched and shows positive coil connection going to a spark plug outlet on the distributor cap.