FORD TRACTOR ELECTRICAL SYSTEM

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

First, regardless if your tractor is 6 or 12 volts, you should carefully inspect the wiring. Look for cracked insulation, splices, bare spots, cuts, etc. What you are looking for on terminals is dull or rusty hardware and any other signs of corrosion. You will usually find at least a few things that require attention. Before you start playing around with the wiring, disconnect the battery ground cable.

It is difficult to impossible to inspect wiring when it is wrapped with electrical tape. Why do they do that? Maybe because it's cheap protection. I use the split corrogated plastic covering that is on most car wiring these days. An assortment of sizes from 1/4" to 3/4" is very inexpensive. Unraveling all that tape is a pain. Removing the harness from the tractor makes the job a lot easier. Loose zip ties can be used to keep the harness together. Individual wires can then be removed and replaced if necessary.

Based on the condition of the wiring on every tractor I have bought, it often makes sense to just start over with new wiring. Don't just throw away the old harness. Even if you plan to buy a complete new harness, the old wiring may come in handy to make sure the harness you bought is the right one. The color coding will most likely be different. Many of the original wires will have one primary color, plus a contrasting stripe. Most harnesses will just have solid color wires. Wire with the correct color and stripe is available from shops that sell restoration-quality stuff. That is a premium cost I prefer to avoid. I use solid color wire matching the primary colors, with heat shrink on the terminal ends that matches the color of the original stripe. A solid yellow wire with black stripe will be yellow with black ends in my new harness. Tractor wiring should always be soldered and completely weatherproofed using marine-grade heat shrink insulation.

HOW TO WIRE A 6 VOLT FORD 8N TRACTOR

Written instructions for wiring a 6-volt tractor, with no theory or confusing diagrams.

The tangled mess of wires on your tractor (or even the brand new harness you bought) may appear impossibly confusing. But the wiring on a Ford 8N tractor is really very simple. The following section should walk you through a complete rewiring job.

The easiest way I have found to help people get their wiring figured out, is to break it down into separate circuits, and deal with them individually.

This walk-thru is based on the original 8N tractor 6 volt wiring. Some earlier 9N and 2N tractors had one-wire generators and used a cutout instead of a voltage regulator. Many of those were later converted to the 8N type generator and voltage regulator, so this walk-through will work for many of those also.

Divide and Conquer

Let's start with the most difficult system and work down from there. Starting with the battery charging circuit will let us begin with the wires in the harness that are noticeably larger in size. There should be three or four large wires that should have yellow colored insulation.

This is easier with loose wires, but you can easily find opposite ends of the same wire in a wrapped harness with a voltnmeter. There aren't that many wires on one of these tractors, so most harnesses should have enough colors it is easy to find the ends.

CHARGING CIRCUIT

1-The large screw terminal located on the end of the generator is the main generator output that charges the battery. It should have a large wire (Yellow with Black stripe) that goes directly to the terminal on your voltage regulator marked "ARM" or "GEN". Hooking the large terminal on the alternator and the smaller terminal on the voltage regulator should also get the harness oriented the right way on the tractor, solving that probiem.

2-There should be a terminal on the regulator marked "BAT". This should have a large wire (Yellow) that goes to one post of the terminal block. On the early, 3-post terminal blocks with a resistor, use the bottom terminal for this wire. On the 2-terminal type, without a resistor, pick either post.

3-From that same post on the terminal block, another large wire (Yellow) goes to the Ammeter. Just pick either ammeter terminal for now.

4-From the other ammeter terminal there should be a large wire (Yellow) that connects to the same Solenoid terminal where the large battery negative cable connects. Some ammeters were "inductive type" and one piece of wire takes care of the previous two steps. The wire just passes through a small loop on the back of the ammeter.

5-Almost done, there are only two small wires left in this circuit. Two small screw terminals on the side of the generator are for "Ground" and "Field". They may not be visibly marked. It's usually stamped on the generator case, but may be very light, rusty, or painted over 16 times. Two small wires go from these terminals directly to the voltage regulator (VR). The ground terminal will be the one that is not insulated from the generator case. The ground wire (Black with Red stripe) connects to the ground terminal on the VR marked "GND". If there is no GND terminal at the VR, just attach this wire under one of the VR mounting bolts. The other terminal is the generator FIELD. This wire (Black with White stripe) connects to the VR field terminal marked "FLD".

DONE!, and that was the most difficult circuit!

IGNITION CIRCUIT

6-Connect a small wire (red) from the coil to the terminal block. If you have the 3-post terminal block, pick one of the two top terminals that connect to the resistor. On the 2-post block use the empty post that you didn't use before.

7-Then, to complete this circuit, connect two wires from your ignition switch to the terminal block. The two ignition switch wires may be color-coded but it makes no difference which way they go. For the 2-post terminal block, it's easy, one wire goes to each post. If you have the 3-post type terminal block, one wire goes to the empty post we have not used yet, and the other ignition switch wire connects to the bottom post with the two yellow charging circuit wires.

DONE!

STARTING CIRCUIT

8-Last, the small starter wire (Red with Blue stripe) goes straight from the small terminal on the Solenoid to the Start Push Button.

DONE! You have just re-wired your tractor.

Ok-Ok, maybe not quite done yet if your tractor has any of the optional lights.

LIGHT CIRCUITS

Headlights, Tail light, and Work light were not standard equipment. All lights were dealer-installed options. Wiring for front and rear lighting is also completely separate from the main harness. There is only one connection to the tractor wiring. There is a short jumper to get power from the junction block to the fused light switch. The light switch has separate terminals for headlights and tail lights. In the original lighting harness there is only one wire to the headlights, and one wire to the tail light(s) from the light switch. All light bulb sockets are grounded inside the housings, so the housings must be mounted to bare metal somewhere to complete the circuit. Rather than scrape off brand new paint and create a rust site, I prefer to bring a ground wire for each light socket all the way back and ground them where the battery cable is grounded to the tractor frame. This takes twice as much wire for the lighting circuits, so most people using a store-bought harness will just scrape some paint where the lights and brackets are bolted together.
The work light is normally on the same wire as the tail light with a switch on the work light housing. To use the work light, the tail light must be on, then you can turn the work light on if needed. A second tail light can also be added to the right side. The opposite-hand fender bracket is available for a second tail light if just one seems wrong to you. I prefer to add the second tail light on my tractors.

Yes, there is a 12-volt version of these written instructions, HERE

Wiring Care and Maintenance

Maybe your wiring isn't a basket case, or it's only been a few months since you re-wired it. There is some standard maintenance we need to keep up with. This is particularly important with the original 6-volt system.

Inspect each connection. If there is any visible corrosion on any connection take it apart for cleaning. A small file works good for shining wire terminals and the base around terminal lugs. Rather than cleaning rusty hardware, it is much better to replace the rusty nuts and washers with new zinc-plated hardware. In a pinch, you can file the face of the nut that touches the terminal. This will work for a little while, but once the plating is gone, the connections quickly rust. Rusty hardware indicates it is time for new hardware with fresh zinc plating. Please, do not use stainless steel hardware or copper washers! It might seem like a good idea, until you find out that stainless steel and copper will cause any plain steel they touch to corrode much faster than normal! Zinc plated hardware is much better in this case. The zinc plating will give itself up to protect plain steel studs, threads, etc. This process is called galvanic action. When different types of metal are in contact with each other and moisture is present, one metal will become sacrificial and protect the other. We want to make sure the one that becomes sacrificial is the least valuable and easiest to replace.

Most of the small nuts are either 8-32 or 10-32 size. Some replacement parts are going to have metric equivalent sizes which are M4 and M5. Put in a supply of those four sizes, and you will have replacement wiring hardware mostly covered.

All switches should be checked with a decent ohm meter to make sure they are in good condition. There are only three, Ignition, Lights, and the Start Button. These switches have typically spent years out in all sorts of weather and can frequently cause mysterious electrical problems. If there is any question or you find any resistance across a closed switch with your ohm meter, replace it.

If your wiring harness is in bad shape, a new harness is easy to buy or make. There are a few cheap replacements with crimped ends, some better waterproof replacements, "Just Like Original" harnesses from somebody like Dennis Carpenter, or several restoration wiring suppliers. The price range for the main engine harness is generally from $25 to $80. You often get what you pay for. Most of the cheapest wiring harnesses are not even waterproof! See my section under "BUYER BEWARE" HERE..

For some odd reason American Wire Guage sizes are basackwards so the smaller numbers indicate larger wire sizes. The sizes I use for 6 volt wiring harnesses are #12(ignition ckt), #10(light ckt), and #8(charging ckt). YES, the wire sizes mentioned here are one or two sizes larger than the original 6-volt wiring and larger than my diagrams show. Why? The diagrams show original wire sizes. The wires don't need to be any larger, but the original wire used on these tractors had rubber insulation. Rubber insulation was much thicker than modern thermoplastic insulation. By going up one or two sizes, I think the wiring LOOKS more original. Plus, the bigger wire is stronger, carries more current, and causes less voltage drop. I use the same sizes for 12 volt wiring for all the same reasons. We could go smaller for a 12 volt system, but if someone decides to switch back to a 6 volt system, the wiring would all have to be changed.

If you want to create your wiring from scratch, please use the correct type wire and terminals. Automotive grade stranded primary wire is a much better choice than solid core building wire. The individual copper wire strands in stranded wire make the wire more flexible. Do not use solid copper building wire for any vehicle wiring. Solid wire can certainly be "trained" to follow precise paths, but solid core wire will transfer all vibration directly to terminals, switches and other components. Solid wire is much more likely to rub against metal parts and damage the insulation. We are replacing the wiring to make it more reliable. Don't use materials or methods that defeat the purpose.

When shopping for wire, if you want the best, marine grade primary wire (for boats) is as good as it gets. Marine grade primary wire has much finer stranding than automotive type, the insulation is thicker, and the copper conductors are tinned to give them better corrosion resistance. If you go that route, you may want to just use the original 6 volt wire sizes. The marine grade wire has thicker insulation so the #8 size wire is over 1/4" in diameter! I did buy and use some #8 marine grade wire for one of my tractors, and it's a little beyond my usual overkill. With marine grade wire, it would be much more reasonable to use #14(ignition ckt), #12(light ckt), and #10(charging ckt).

Here's a photo of three pieces of No.12 gauge wire. The top one is solid core building wire. Don't use that. The bottom one is automotive grade primary wire. the insulation should say "oil resistant". The middle one is premium marine grade with very fine, tinned copper stranding. Notice the thicker insulation on the middle piece. This becomes even more noticable on larger wire sizes below.

These are No.10 gauge wire. Marine grade and automotive grade.

These are No.8 gauge wire. Marine grade and automotive grade.

Here they are all together. The No.8 size is shown for grins. That is bigger than anything needed on a tractor unless you are planning to have some really powerful amplifiers for a stereo that will rock the whole neighborhood.

Try to stay as close to the original color coding as possible. The trouble is the original wiring was not plain solid color insulation, some of the wires were solid color with a contrasting stripe.

The original color wire can be bought from antique restoration suppliers, for a premium cost (There, that was for the originality police). My method of dealing with the contrasting stripe wire is to buy the correct solid color wire and then use colored heat-shrink tubing that corresponds to the stripe. So a "red with blue stripe" original wire would become "red with blue ends" in my harness. I do not "RESTORE" old tractors, my mission is to keep old tractors working reliably without spending gobs of cash trying to stay with strictly original materials.

If you have lights, these will be the longest wires on your tractor, and they carry the most load, so voltage drop is a concern. I have run #10 AWG wires for 6-volt lights so they will be as bright as possible. That may be overkill even on a 6 volt system. Connecting the light switch hot, ahead of the ignition switch, makes is so the lights can be turned on with the key switch off. This is a convenience that might also save the coil. It certainly saves wear and tear on the ignition switch.

The pigtail that goes from inside to outside a light housing does not need to be any larger wire than will carry the load of that light fixture. A typical high beam headlight bulb is 55 watts. Even on a 6 volt system, a 55 watt high beam is only 9.2 amps. A No.18 wire is good for 14 amps so you can probably run the high and low beam elements at the same time on a No.18 wire. Don't do that. Most dual element bulbs are intended to run one or the other, not both elements continuously. The bulb will get too hot. I generally make my pigtails using No.16 or 18 stranded wire with high temp insulation salvaged from old appliances and light fixtures. The wire is small enough a set of 2, or 3 can be put together with a heat shrink jacket and still fit thru that hollow headlight bolt. Use 3 wires if you want a ground and separate hots for high and low beam. Putting butt splice connectors just inside the fender provides a removable connection to the larger circuit wires that carry the load of all lights.

LIGHTS ON A BUDGET

The originality police will have a heart attack with this one. Finding original lights used, or new restoration grade from someone like Dennis Carpenter has gotten very expensive. Most of us have more things on our list than we have money to buy. Bolt-on accessories such as lights are one item that can be shopped way down in price with good results.

I've been able to find several round metal and even plastic trailer lights that seem reasonably close for tail lights.

The original pigtail will be replaced with a new one as described above.

These were for my 2N tractor. Metal or plastic can be painted, and have survived for years on my tractors. They look better with the bolts turnned around so washers and nuts are inside the housing.

Headlights have been much harder to find. Used originals turn up regularly on eBay but they just seem to get more and more abused and expensive. Most aftermarket round headlights are the wrong shape or way too big. My most recent find is another Harbor Freight item. These "off-road" lights are the right size, and the shape is very close. They even come with 12-volt H3 bulbs! I've bought H3 conversions for 9N headlights that cost more than these did.

The photo shows one headlight as-purchased for $10 with an ugly double closure-ring and exposed wire harness. It was easy to trim the gasket down and do away with one trim ring.

Side by side the HF version is not quite as pointy in back.

The exposed wiring was really well done, almost good enough to keep, but the Ford hollow headlight bolt fits perfectly, so the new wire pigtail can be concealed. A rubber or stainless plug will need to be scrounged for the hole in the housing. It's not in a location that will be easy to see.

The H3 bulb conversion housing has a flat, clear lens that some people may not like or maybe we are shopping for a 6 volt tractor.

Just for grins, This photo shows one with a standard 8N 6-volt sealed-beam bulb and trim ring. The chrome trim rings are not as wide, but could probably be made to work by trimming the rubber gasket differently. My current project is 12 volts, so the H3 kits will work fine.

A 1/2" nickle chrome plated hole plug is a perfect fit in the external wire hole.

DID YOU POLARIZE THE GENERATOR ?

WHAT? Yep, I immediately glazed over with a blank stare the first time someone asked, "did you polarize it". These 6-volt systems can be a little wierd, even for someone who has worked on all sorts of vehicles for well over 30 years. I thought this might be another barnyard spoof or snipe hunt for the rookie tractor owner. Here we go again, back to the web browser to do a few searches. The simple explanation is that the 6-volt generator can get confused when it has been disconnected from the battery. The generator may "forget" which way it was wired.

When you are finished with the wiring, make sure the ignition switch is OFF and both battery cables are connected and ready to go.

Before you turn the key on or do anything else, you need to polarize the generator. On the 8N tractors, we can use a jumper wire or a flat blade screwdriver to momentarily short between the "BAT" and "GEN" terminals on the regulator. Sometimes they will be marked "BAT" and "ARM". Make a spark and it's done. Make sure to short BAT to ARM and not to FLD. If the three terminals are all in a row, they should be marked B-A-F. BAT and ARM are right next to each other.

The polarization mentioned here should be done any time you notice the generator is not charging, and you just did some sort of repair or maintenance where the battery or generator was disconnected. Often the generator will maintain correct polarity without doing this step, but occasionally it will need to be polarized to re-establish correct polarity with the tractor wiring.

If you have one of the later 6-volt Ford or other tractors, it may have the type "B" system. Look for the regulator terminals to be marked A-F-B. If the BAT terminal is not right next to the ARM terminal at the regulator, this is a type "B" system. The "B" systems take a little more work to polarize. Disconnect the FLD terminal, touch the FLD terminal to BAT, then reconnect the FLD terminal.

If your N-Tractor has the original type voltage regulator, those do not have three terminals in a row, clearly marked. The terminals are scattered around on three sides. There is one terminal by itself (BAT). Then there will be two terminals together. The closest one of those to the BAT terminal is ARM. The 4th terminal on most of the regulators I have seen is GND. It's easy to tell from the others. Usually a terminal soldered directly to the metal base. If there is no ground terminal, connect the ground wire to one of the mounting bolts.

Here's a photo of an original type Voltage Regulator. The terminals on this one are not in a row, and they are not marked, so I labeled them on the photo.

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If you came here looking for 8 volt conversion info or regulator adjustment info. I've published what I have on the subject, HERE

A 12-volt conversion will not fix very many of the things that cause a tractor to be unreliable. The simple fact remains that these old 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 they will fail. Changing the voltage may increase the time between maintenance, but also increases the potential damage when there is a failure. More voltage equals more energy. Things that just looked dirty at 6 volts are often melted and useless when they fail at 12 volts. Delayed maintenance equals more costly maintenance and repairs that might have been avoided with a little elbow grease.

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