FORD TRACTOR 12 VOLT CONVERSION WITH ALTERNATOR

The 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.

There are several 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. 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. Newer one-wire alternators have solved the low RPM excitation problem. They cost more than the garden-variety 3-wire 10SI but I think it's worth it for the simpler wiring. There are also rebuild kits that replace the voltage regulator in a 3-wire Delco with a low-RPM 1-wire unit. That is what I used on my 46-2N tractor.

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. In some cases the pulley from your old generator will fit the alternator! 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. Then the pulley should pull right off the shaft. Careful! Some of the generator pulleys may be threaded onto the shaft. The larger generator pulley will also spin your alternator slower than the correct 2" pulley. Your new alternator may not charge at idle so if you idle around doing things like parades or hay rides, spend the money and get the smaller 2" pulley.

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 alternator 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.

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 works great.

If you choose a pre-packaged conversion kit, you will spend more money, but you should get the correct alternator, pulley, belt, brackets, coil, 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.

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, square design, front-mount coil.

One way to get this right is to measure the resistance of the actual coil you plan to use, and make sure you have between 3.5 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. You need a good ohmmeter. Don't forget to zero your meter and/or have good batteries in it.

Someone contacted me recently who was using an inexpensive ohmmeter. He was reading almost 2 ohms through the coil, but when he shorted the ohmmeter leads together, he got a readiing of 0.8 ohms! Shorted leads should be -ZERO- ohms. Perhaps you can subtract the shorted reading from the reading through the coil, but that meter is nearly useless.

Most 6 volt coils measure around 0.5 to 1.0 ohm and most 12 volt coils measure around 2 to 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 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 both sets of leads together.

If you don't have a reliable ohmmeter, most meters are reasonably accurate on the amps scale. There is still no substitute for a decent meter. Figure the cost of replacement coils and why would anyone trust a $20 meter for this kind of work? The other way to go wrong reading amps is you need a fully charged battery and good connections. A weak battery lowers the voltage and current. Bad connections add resistance which also lowers current.

The best ammeters have an inductive pickup. The meter jaws clamp around the wire going to the coil. Turn key on with the points closed and read current. Don't leave the key on! Another way to do this is on the bench if your ammeter only has test leads. Run a wire from the positive post of a fully-charged battery, to the resistor(s), then to the coil terminal. Then, use your meter leads to complete the circuit from the coil back to the battery negative post. Don't rconnect any longer than it takes to read amps. You want to try different resistors until you get 3-4 amps. 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. Do not hook this circuit up and leave it! You will fry the coil. Hook everythign up but one wire and make contact just long enough to read your ammeter. We want about 3 to 4 amperes. Less=poor high speed performance, more=short point life &/or burned up coil. If you are over 4 amps, add more resistance.

The later round-can type coils on the side-distributor 8N tractors are much more durable than the square-can type coils. Many of the later 8N tractors use a 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 somewhere 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 accessory 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-SHOOTING

After 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. The Ford Tractor solenoid is not the same as the automotive types that look very similar. For more information about the solenoid CLICK HERE.

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, and you don't know which one is bad, 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. If you don't have a decent ohmmeter, just replace the switches, they are not expensive.

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