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 rusty hardware and any other signs of corrosion. You will usually find at least a few things that require attention. But, before you start playing around with the wiring, disconnect the ground cable at the battery.
Based on the condition of the wiring on every tractor I have bought, it's probably most appropriate to put this section next:
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.
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 pieces of large size wire that should have yellow colored insulation.
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".
2-There should be a terminal on the regulator marked "BAT". This should also 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. On the 2-terminal type, without a resistor, pick either one.
3-From that same post on the terminal block, another large wire (Yellow) goes to the Ammeter.
4-From the other side of the ammeter 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 diffcult 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.
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.
Yes, there is a 12-volt version of these written instructions, HERE
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 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. Plus, if someone decides to switch back to a 6 volt system, the wiring will be large enough.
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 also 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 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 drop back one wire size from the sizes indicated above. The thicker insulation makes the #8 size over 1/4" in diameter! I did just make a 6 volt 8N harness using the #8 Marine grade wire for the charging circuit, and it's a little beyond my usual overkill. With marine grade wire, it would be 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.
Try to stay as close to the original color coding as possible. The trouble here is that the original wiring was not plain solid color insulation, much of the wiring used 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 run #10 AWG wires for 6-volt lights so they will be as bright as possible. I wire the light switch hot, ahead of the ignition switch, so I can turn the lights 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.
Another wiring improvement is to run two wires to each light. One wire connects to the light switch for power, the other brings the ground all the way back so you can ground it to the same point the main battery ground cable connects to the frame. This is only a couple of extra wires to run, but I believe the improvement is worth it. Some people think I have 12 volt lights on my tractor!
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
Doing a 12-volt conversion will not fix all of the things that will cause an electrical system to fail. 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 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. Delayed maintenance equals more costly maintenance and repairs that might have been avoided.
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