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The Easy 12 Volt Conversion

All N-Series Front-Distributor Tractors - Ford-Ferguson 9N, 2N, and Ford 8N

Tractor Wiring 101 For The Electrically Challenged.

This is condensed written conversion instructions with no confusing diagrams or electrical theory. Nobody really wants to know that "stuff" anyway, right? GRIN.

The tangled mess of wires on your tractor (or even the brand new harness you bought) may appear impossibly confusing, but the wiring on these old Ford tractors is really very simple. The following should walk you through a complete 12-volt rewiring job with a 1-wire alternator. All LEFT, RIGHT, FRONT, BACK directions are based on the operator sitting on the seat looking foreward.

Before you start messing around with the wiring, disconnect the ground lead at the battery. Better yet - Disconnect both battery cables, take the battery out, and put it on a charger/maintainer. If you don't have an automatic 12 volt battery charger, get one.

I will assume your current wiring system is the typical complete hack job. Often you are dealing with a failed 12 volt conversion that maybe never worked.

I will assume you have already dealt with the physical issues of mounting a 1-wire alternator with the correct 2" pulley, the correct belt, serviced the distributor, and installed a 12-volt replacement front mount coil. If not, those are covered elsewhere on this site. Check the index.

Take apart all wiring connections and remove the old wiring. Nuts and washers that look shiny can be twisted loosely back onto the studs. Collect rusty, or rounded hardware, take it to the hardware store, and buy new shiny, zinc-plated, hardware to replace it. Do not buy stainless steel, copper, or any other metal hardware. Most hardware stores have a place where you can match up threads and sizes, or someone who will do that for you.

LOOK at the surface around each post where the terminal goes. If the surface isn't shiny, make it shiny. A small file will work, but don't mess up the threads, if you are re-using hardware. Lay the back side on the file and slide with your finger to shine them up.

Remove the voltage regulator and anything else that won't be used in the new system. Check all switches with an ohm meter or just replace them. They aren't that expensive. Make sure the ignition switch is turned OFF before and after mounting it. Check it twice with a meter or test light.

Buy a new 12-volt front distributor 1-wire harness. You get what you pay for, but even a cheap harness is better than what you started with. Look at the harness. Each wire has two ends. They should be color-coded so you can find the two ends of each wire. A cheap harness lay leave you playing where's waldo with four large yellow wires. No problem.


Let's start with the most difficult system and work down from there. Starting with the battery charging circuit will also let us begin with the wires in the harness that are noticeably larger in size. There should be three or four lengths of large size wire that will usually have yellow colored insulation. Sometimes it's Red. Look for one end of the harness with two wires. One large Yellow (usually with Black stripe) and one small red wire. That will be the front end of the harness. Front distributor engines usually have a wiring "tube" along the top of the engine. These two wires go through that tube and come out at the front of the engine. If you don't have a tube, just lay this part of the harness on top of the engine for now, with the wire terminal ends at the front.

Look near the back of the engine for a piece of harness with two wires, that split off from the main wire bundle. One large yellow wire with a very large ring terminal and a much smaller red with blue stripe wire. Let those hang down by the starter for now. This confirms we have the harness turned the right way. If you have the yellow wire with the very large terminal end at the front, flip the harness around so the large terminal is down by the starter.

Find the screw terminal on the back of the alternator. This is the main output that charges the battery. Connect the large yellow wire we laid at the front of the engine, to this screw terminal, hand-tight for now.

Find the other end of that same wire. It goes directly to a terminal on your junction block on the back of the dash. Lay the harness out so this wire ends up on the left side of the dash behind the ammeter. That is where the terminal block is located.

The junction block has a resistor mounted to the top two terminals. Connect the other end of the alternator charging wire to the empty bottom post on the terminal block. Before twisting the nut on this one, STOP. Look at your ammeter. Does it have two screw terminals, or is there just a small loop of metal on the back? Some ammeters were "inductive type". They do not have terminals, there is only a "loop" on the back. In this case, one piece of wire takes care of the next two large yellow wires. Rather than connecting to the ammeter, the wire just passes through the small "loop". I will assume the alternator is the standard type since most wiring harnesses make the same assumption.

Look for a very short piece of the large yellow wire about 6 inches long. One end goes on the junction block terminal, with the wire from the alternator. The other end goes to the Ammeter. Pick either ammeter post for now. We are still attaching hardware loose.

There should only be one large yellow wire left. We laid one end near the starter a few minutes ago. This wire connects to the large solenoid screw terminal with the battery cable. The other end connects to the remaining post on the ammeter.

Charging circuit is DONE! That was the hard one!


Go back to the front of the tractor. Connect the small wire (red) to the terminal on top of the coil. The other end of that red wire will be back by the junction block. Pick one of the two terminals that connect to the resistor for this wire.

To complete the ignition circuit, you simply connect the two wires from your ignition switch to the junction block. One wire goes to the bottom post and the other connects to the opposite side of the resistor from where you connected the red coil wire.

Ignition Circuit is DONE! See how easy this is!


Find the small start wire (usually Red with Blue stripe) down by the start solenoid. This one goes from the small terminal on the Solenoid to the Start PushButton.

That's It! All of the small wiring is connected. Now, the most important step is to go back and attach the harness with tie wraps or proper clips so the terminals are not under any tension. The wiring harness must be completely supported and tucked out of sight as much as possible, so it cannot be damaged by sharp edges, tree branches, or hot exhaust manifold.

Once the harness is properly attached, go back through these steps and snug each terminal. Do not over-tighten these little nuts!


By now that battery should be fully charged. Are you sure the ignition switch is still OFF? Check it and make sure or we may weld a set of points and fry a brand new coil! Set the battery in place, so the cable from the solenoid will reach the Positive + battery terminal post and the ground strap connects to the Negative - terminal post. Do clean the place the ground strap connects to on the frame. A shiny metal to shiny metal connection is necessary.

Do use proper brackets to hold the battery in place. Original type brackets work best, but most universal brackets can be adapted to be nearly as good.

No conversion will permanently fix all of the things that will cause an electrical system to fail. The simple fact remains that these tractors do require more frequent maintenance than modern equipment. Open connections and unsealed switches are attacked by the environment and deteriorate over time. If you don't take things apart and clean the connections eventually they will fail. Changing the voltage may increase the time between maintenance but also increases the potential damage that can be caused. More voltage equals more energy to dissipate. Things that just looked dirty at 6 volts are often melted and useless when they fail at 12 volts.

Late 8N Side Distributor Tractors, NAA, and newer

The conversion wiring is basically similar for all newer tractors. Easier is some ways, because these tractors can all use a true 12-volt round can type coil. They do not use an ignition resistor with the original 6 volt system, so there are fewer options and much less confusion. The generator/alternator, distributor, coil, and solenoid move around on the various models, so the harnesses are all slightly different, but the basic wiring is the same.

RETURN - to main TUNE-UP page or go to the next subject COOLING SYSTEM


Content and Web Design by K. LaRue — This Site Was Last Updated 02 FEB 2023.

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