FORD 8N TRACTOR 12 VOLT CONVERSIONThis is my page of notes and diagrams for converting Ford 8N tractors from 6 volts Positive Ground to 12 volts Negative Ground.FIRST There are some good reasons to convert your tractor to 12 volts, but there are at least as many reasons for keeping the original 6 volt system. If you have already made up your mind, and are positive that you are capable of doing the work properly yourself, read on. If your are the least bit unsure of your reasons for wanting to go with a 12 volt system, PLEASE review the additional information I have provided on the 6 volt vs 12 volt systems HERE. The diagrams on this page show the most successful way that I have found to convert your 6 Volt Positive Ground Tractor to 12 Volts Negative Ground. If you are interested in some of the less common conversions I have provided two examples HERE DESCRIPTION The first surprise for many is that the 6 volt starter, solenoid, switches, ignition coil, points, and most of the wiring can remain. This is because these components are insulated well enough to withstand a lot more than 12 volts. The starter will NOT spin in reverse when you change from positive to negative ground. It is a series-wound motor and will spin in the correct direction regardless. Bulbs will of course need to be replaced with 12 volt bulbs but the only other item that must be protected from the higher voltage is the ignition coil. Some people prefer to just use a 12 volt coil instead of trying to figure out how much resistance to add to the ignition circuit to protect the 6 volt coil while still providing a good hot spark. Some believe the 12 volt coil delivers a hotter spark. In some cases that might be true, but it has more to do with the wiring than the coil itself. Properly wired, the spark from a 6 volt coil is every bit as HOT as the spark from a 12 volt coil. Either one will knock you on your butt if you get careless. CAUTION My first 12 volt conversion worked great, but it was too much of a departure from the original wiring. I didn't have much to base it on, the wiring on my tractor had been patched and taped together numerous times. So I pulled all the old wiring off and started from scratch. I have extensive training in AC and DC systems, I have designed and in many cases built everything from go carts and race cars to high-rise office buildings. I have done both residential and commercial electrical work, and have been working on just about every type of vehicle there is for over 30-years. I could easily re-wire one of these tractors myself. What I didn't think about was the next owner of my tractor or anyone who might use the information I provided on this page to re-wire their tractor. SHAME on me! This ground has been thoroughly plowed so many times over the last 40-plus years that NOBODY should do a 12 volt conversion from scratch. All you will be doing with your custom wiring job is creating a problem for the next person to work on your tractor, unless they can read your mind and see exactly what you did. Please, stay as close as you can to the original wiring, or simply buy a new 12 volt wiring harness. The following diagrams show the original 6 volt wiring and then a 12 volt conversion for both the early 8N front-distributor Ford tractor and the late 8N, side-distributor Ford tractor. These diagrams have been revised to stay as close to the original wiring and use as many of the original switches and accessories as possible. EARLY 8N FORD TRACTOR FRONT DISTRIBUTOR - 6 VOLT EARLY 8N FORD TRACTOR FRONT DISTRIBUTOR - 12 VOLT
LATE 8N FORD TRACTOR SIDE DISTRIBUTOR - 6 VOLT
LATE 8N FORD TRACTOR SIDE DISTRIBUTOR - 12 VOLT
NOTES TO THESE DIAGRAMS To save any of these to your computer simply RIGHT CLICK on the image and select SAVE IMAGE AS... Then give it a path and filename or select the default. Some browsers are different but yours should have an option similar to this one. All of these diagrams show the light circuit connected ahead of the ignition switch for two reasons. One reason is so you can use the lights with the engine off and not cook the coil. The second reason is to reduce the amount of current going through the ignition switch. The 12 volt conversion diagrams show a diode that can easily be soldered in-line and protected with a piece of heat-shrink. This diode allows use of the original 2-wire ignition switch and does not require adding an indicator light. If you prefer, you can substitute a bulb in place of the diode. Use one that is equal to the ones typically used for side-marker lights. My 12 volt conversion diagrams have one minor difference from many of the other conversion diagrams you will find. Most people just show a jumper from the No.2 terminal on the alternator directly to the BAT terminal on the alternator. I believe it is important to make the voltage sensing connection as close as possible to the accessory terminal so the alternator senses and reacts to system voltage rather than alternator output. Since there is already a wire in the 8N harness that goes all the way to the dash, why not use it? Not shown on the diagrams are some small wires to the instrument lights in the backlit aftermarket gauges I used. The bulbs were there, so I wanted them to work. I added the gauge lights to the headlight/taillight circuit. Other upgrades you might want include: A separate switched work-light. Flasher for the tail-light circuit. A second tail-light. Amber front lights. Stereo, CD, DVD, 52" plasma screen... If you feel the need, Go for it, it's your tractor. The originality police won't like it, and I might agree if you were working on a 39-9N or one of the other rare tractors. But this page is primarily concerned with tractors that work hard. Somebody else can create a site for restoration work. ALTERNATOR CONNECTIONS
There are four connections on the Delco 10SI, internally-regulated alternator. The connections are the large output terminal (BAT+), the ground terminal (GRD-), and two connections usually labeled 1 and 2. Terminal #1 is the "exciter" or "field" wire. Terminal #2 is the "remote voltage sensing wire". There should be no confusion regarding the BAT+ connection. This large insulated threaded terminal post is the one that provides all the current for your accessories and to charge the battery. The GRD- connector is another large threaded terminal post, but this one is un-insulated. This terminal is usually not needed. Terminal #1 Most successful 8N Tractor conversions connect the field wire from this terminal directly to the switched side of the ignition key using an in-line resistor, bulb, or diode. If you use a diode, make sure you connect it the right way so it allows current to flow towards the alternator. Terminal #2 Most successful conversions simply run a short jumper wire from Terminal #2 directly to the alternator output (BAT+ terminal). It may work OK that way, it is certainly the easiest way to do it, and it does not hurt my feelings if you want to do it that way. However, this is the Remote Voltage Sensing Wire and it really should be connected to the main accessory post. The ideal connection would be right where the ignition switch, light switch, and any other accessories are connected to the main terminal block. The #1 and #2 terminals on the Delco 10SI alternator should be connected to your wiring with a special plastic 2-wire connector. You can use individual female crimp-on connectors for each wire, but the proper clip can usually be found in your local auto parts store near the miscellaneous electrical sockets and other replacement electrical parts. Using the proper connector is a more professional solution and also gets you the integral plastic clip that keeps the connector from shaking loose and falling out. CAUTION - AGAIN There are many different ways to convert your tractor to 12 volts. As I mentioned above, in order to protect the sanity of the next person to work on your tractor (including you) it is best to try to stay as close to the original wiring as possible. Do some research into the actual alternator you plan to use. But beware, there are plenty of diagrams and instructions on the web that are just plain wrong. My diagrams are, of course, practically perfect in every way, GRIN. The 12 VOLT CONVERSION WITH AN ALTERNATORThe steps to any 12 volt conversion using an alternator are basically: remove the old generator and regulator, create or buy brackets to mount the alternator, run or reroute a few wires to the alternator, replace 6 volt bulbs with 12 volt bulbs, and add a voltage dropping resistor in the ignition circuit. Many sources provide pre-packaged kits for converting the Ford 9N, 2N, 8N tractors from 6 volt Positive Ground to 12 volt Negative Ground. All that I am aware of use the same Delco 10-SI alternator. Sadly, there are a lot of people cashing-in on 12 volt conversion kits who don't seem to care if you never get the system to work properly. Virtually every conversion kit out there can be made to work, IF you know what you are doing. You might have to buy some additional parts. A good conversion kit should come with complete instructions as well as a help line or on-line tech support for those non-standard problems that will turn up on a 50-plus year old machine. Most everyone recommends using the Delco 10SI alternator. This is because GM used this same basic alternator on just about every vehicle from the '60's through the mid '80s. So they are inexpensive, sometimes free, and the required connections are simple. Delco also makes a One-Wire alternator that hot rodders have used for years in their conversions, but I do NOT recommend using that alternator on a tractor engine. Some have used it with success, but the typical tractor engine does not turn enough RPM for that alternator to work properly.Update, there are some newer Delco type one-wire alternators that claim to have solved the low RPM excitation problem. You might be able to find a GM 10SI application that comes with a pulley that matches the wider belt on your tractor. If not, any 10SI alternator will work just fine, and you can buy the correct pulley from someone like just8ns.com. Update, A friend told me that you can use the pulley from your old generator! Apparently, the shafts are the same size. You will need an impact wrench to remove the bolt holding the pully. I am sure there are other ways, but an impact wrench works best. Careful! Some of the generator pulleys may be threaded onto the shaft. The reason any 10SI alternator will work is that, even though there were dozens of different applications, the only real differences are the pulley (you will be changing that) and the phasing. Phasing is the physical location of the wire connections in relation to the mounting brackets. This can easily be changed by simply removing the bolts holding the housing together and rotating the housing until the bolt holes line up again and the connections are where you want them to be. DO NOT pull the case apart when doing this! The brushes are spring-loaded and if they come out you will have to find something to hold them in place while you slide the two halves back together. This can be one of those aggravating tasks that ruins an entire afternoon. OK, I will assume you are like me and have already dissassembled your alternator and separated the halves. Maybe you dropped it or you have a helper who sometimes isn't so helpful? If your brushes have already been let out of their little cages, any straight piece of stiff wire can be used to thread through the holes and hold the brushes in place while you put the two halves of the case together. A straightened paper clip will work. If you choose a pre-packaged conversion kit, you will spend more money, but you should get the correct alternator, pulley, brackets, ballast resistor and everything else you need in one box with instructions! If you prefer a challenge, and want to save money doing this from scratch, do your homework. Please, don't take the first diagram you find (mine included) and start re-wiring your tractor. Even with the kits, if you want full benefit out of your new alternator see below. IGNITION RESISTANCE This may be the hardest part of a 12 volt conversion to get right and keep right. Even if the original conversion works properly, the first time someone needs to replace the coil there are often problems. There are several different replacement coils available and we cannot depend on the markings on any of the coils. The ignition circuit is a balancing act between having enough resistance to protect the coil but not so much resistance that we no longer have a good hot spark. This is particularly critical with the weaker front-mount coil. All 12v coils aren't created equal. Perhaps the easiest way to get it right is to connect the coil & a good ammeter in series across a 12v battery & measure the current. We want about 3 to 4 amperes. Less=poor high speed performance, more=short point life &/or burned up coil. If much over 4amps, then add ballast resistor. 5A is too much. Another way to get this right is to measure the resistance of the actual coil you plan to use, and make sure you have between 3.6 and 4.0 ohms of total resistance in the circuit. The correct way to measure the resistance of a coil is by connecting an ohmmeter to the two screw terminals on a round can coil or to the screw terminal and the coiled spring terminal on a square front-mount coil. Don't forget to zero your meter and have decent batteries in it. Most 6 volt coils measure around 1.0 ohm and most 12 volt coils measure around 3.5 ohms, but individual coils seem to vary widely from those values. Subtract the actual coil resistance you measure from 4 ohms to figure out which resistor you need. The correct type of resistor is a wire-wound ceramic resistor with a power rating of at least 50-watts at 12 volts DC. If you cannot find an odd size, you can wire two in parallel to get half their rated value. So, to make a 1/2 ohm resistor, lay two 1.0 ohm resistors side-by-side and twist the leads together. The later round-can type coils on the side-distributor 8N tractors are much more durable than the square-can type coils, so many of the later 8N tractors are able to run a 3.5 ohm 12 volt coil with no additional resistor in the ignition circuit. However, if we are using a 6 volt coil or any of the square-can coils we will usually need to add a resistor with a rating between 1/2 and 3.0 ohms. If you are one of those people having problems with your 12 volt conversion, and the whole question of ignition resistance seems too complicated, you may benefit from some additional explanation, theories, and information I have provided HERE. CAUTION !I have seen very few 12-volt conversion diagrams with fuses. This is one "modern" safety improvement that in my opinion should not be omitted. Especially when you are going to the trouble of rewiring something. The most valid reason for converting to 12 volts is so you can use higher-wattage bulbs and modern 12 volt electrical accessories. You are going to need a place to connect those new accessory circuits. I added a fuse block with space for a couple of extra fuses. If you want your wiring to appear more genuine, you could conceal in-line fuses in a few critical locations. It might save your tractor, garage, shop, house, or family! TIPS AND TROUBLE-SHOOTINGAfter rewiring, the engine starts and runs, the celebration begins, but when the key is turned off, your engine just keeps on going. This is one of the more common problems and of course the timing really stinks. You just put away your tools, opened a beer, and your recliner is calling. You turn the switch off, off, off, what the...! You have probably connected the No.1 FIELD wire for the alternator to the same 12 volt source as the ignition wire to the coil. If so, the alternator will back-feed power to the coil with the key in the off position. Even if you remembered to put a diode in the field wire, it may be installed backwards, or it could be a bad one. Sometimes these diodes are bad right out of the box. If you decided to use a bulb or resistor instead of a diode, it might be too big and is not providing enough resistance. Definitive proof is if the engine that is still running with the key in the off position dies when you remove the two-wire connector from the alternator. To fix this you need to add, reverse, or replace the diode (one way valve) in the wire between the alternator Terminal No.1 and the ignition circuit or use a lower wattage light bulb. If you are replacing the ignition switch, PLEASE resist the temptation to use an automotive switch with a spring-loaded start position. The original solenoid on your tractor will not work with this type of switch and if you change the solenoid to wire it this way, you will be bypassing the neutral safety interlock. If that is the only switch you can find, ok just don't connect anything to the START terminal. There are very few safety devices on these old tractors, so there should be no doubt that the neutral safety interlock is NECESSARY. Most people will replace the 6 volt headlight bulbs with 12 volt bulbs. If you don't want to spend the money for new bulbs, you can wire any pair of 6 volt bulbs in series. Run the hot wire from the light switch to the first bulb, connect the other lead from the first bulb to the second bulb, then the second lead from the second bulb should be grounded. Two 6 volt bulbs wired in series equals 12 volts. It will work, but the disadvantage is that if either bulb burns out you have no lights, similar to cheap christmas tree lights. Before you just start ripping the old wire off your tractor, carefully label and remove the old harness. Then you can measure wires in the old harness to cut your new wires the correct length. Put the old harness away in a box with all the old 6 volt stuff. This box could be a real prize for someone trying to restore one of these tractors. All switches should be checked with a decent ohm meter to make sure they are in good condition. They have typically spent years out in all sorts of weather and frequently are the source of many electrical problems. If you find any resistance across a switch, replace it. Here is a Close-Up of the alternator installation on my front distributor 8N tractor. The bottom bracket is a simple "H" with the bottom legs bolted to the stock generator mounting point and the top legs bolted to the alternator base. I left some room for washers to adjust the exact position to line up the belt. You will want to use some type of locking nuts on these bolts. I used the nylok kind with the nylon locking ring built into the nut but crown nuts with cotter pins or safety wire would also work. Vibration just seems to shake any non-locking hardware loose. I indexed my alternator so the connector was on top to keep the wires away from the manifold. It would have been better to rotate it so the connector is at the bottom and better protected from weather. Water running off the hood killed my alternator within 6 months! The top bracket is a piece I found that I had to cut and weld so it would attach to a convenient head bolt. I was very disappointed in this part, the slotted part should have been in a arc for it to work properly with the way the alternator swivels. Look for an original bracket from an older chevy. These have the curved slot and can be easily modified to work on your tractor. When I got done, the alternator pulley ended up in the exact same place as the old generator pulley, so I was able to use the original length belt. B U Y E R |
