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DEEP DELCO®
This page will dig a little deeper into the proper electrical connections for the Delco® alternator most 12 Volt conversions will use. There are literally hundreds of different alternators that have been used in 12 volt conversions. Any alternator can be made to work as long as you how to do the wiring correctly. The wiring can be as simple as hooking up a single No.10 AWG wire to six or more connections on some modern alternators. The Delco® 10-SI alternator is by far the most common choice for conversions primarily because new or rebuilt versions cost much less than any other choice. It is the ONLY alternator I will claim to know much about. I could figure out how to get a Toyota alternator to work on a Ford tractor if I had to, but I don't WANT to. Even if a different brand of alternator is free and in perfect condition, it will eventually fail and need to be replaced. That is not a good time to find out we need to spend $180 and wait two days for a replacement or rewire the tractor AGAIN so we can use the cheap and readily available Delco®. Some people may balk at putting a GM® alternator on a Ford®. I will try to save you some money and time. After digging through several catalogs, what I found was that the best choice of various alternators was on the '80s Mustangs® and some other models. Guess what, from four feet away, the Motorcraft® alternator might as well be a twin to the Delco®. But it costs nearly $200 bucks. Other psople like the 1-wire Delco® alternator. It is easier to hook up (only 1 wire) but I do not like that alternator for a vehicle that will do a lot of idling or low RPM work. Some of this will be a repeat of the condensed version on my 12 volt conversion page. Click "12 volt" on the navigation bar on the left side of this page if all you want or need is the short version and wiring diagrams. Delco® ALTERNATOR WIRING CONNECTIONSThe Delco® 10-SI is often referred to as the "TWO WIRE" alternator. This is because many successful conversions only connect two wires from the vehicle wiring system to the alternator. There are really four connections on the back of the (two wire) Delco® 10SI, internally-regulated alternator. There are two large threaded stud connections. The insulated output terminal (BAT+), and the uninsulated ground terminal (GRD-). Then there are two small recessed male spade lug 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. On most Ford Tractors this terminal will be connected directly to the accessory post on the main terminal block and from that same post to the accessory side of the Ammeter Gauge with #10 or even #8 AWG wires. The other side of the Ammeter Gauge should just have one #10 or #8 AWG wire that goes to the starter solenoid terminal where the large Battery positive cable is connected. The GRD- connector is nearly always left bare. However, you might need a ground wire if you are mounting the alternator to your engine block with something other than steel or aluminum brackets. Another reason would be if your engine is electrically isolated from the rest of your wiring, such as in a wooden or fiberglass boat. Terminal #1 On most OEM installations this terminal is connected to a switched 12 volt accessory source through a dash-mounted pilot light. This wire provides the "excitement" current to the alternator field windings. Leave this disconnected, and MAYBE your alternator will self excite, maybe not. Revving the engine might get it charging, but if you let it slow idle a bit, it can slip back into discharge (been there, done that). It's also probably not a good idea to regularly run a cold tractor engine at full speed just to get the alternator to start charging. Some conversions connect the field wire directly to a switched accessory source, others recommend connecting to the ignition switch using a resistor or diode. But that was not the way the Delco® alternator was designed to work. The standard incandescent dash LIGHT BULB is important. I will skip the technical theory and just say that there are properties inherent in a light bulb that cannot be properly duplicated by a resistor or diode. Some folks replace the original two-wire ON-OFF key switch with a new OFF-ACC-IGN switch that has separate terminals for Battery, Ignition and Accessory. This allows you to power the Ignition and Field circuits from two separate terminals, preventing the alternator from backfeeding the ignition when the key is turned off, and allows the alternator dash light to work properly. How The Dash Light Works KeyOFF: No power to the ignition or alternator. If this isn't switched off, it will run the battery down and probably fry the coil. Key ON with Engine Stopped: The light "sees" a 12 volt drop across it, lighting it. One end is on battery 12 volts, the other end is on the motionless alternator - same as if the alternator failed. If the light does not glow when the ignition is turned on, you probably have a deal battery or the bulb is bad. Key ON with Engine Running: With a good alternator the dash light should go off as soon as teh engine starts. Both sides of the light now see 12 volts, so no current shoudl be passing through the bulb. Voltage across the bulb is 0, no glow. If there is a failure in the charging system, it will upset the balance and the light will glow. The brightness of the light can be an indication of the magnitude of the failure. Dash Light Installation Of course your 50+ year old tractor is not equipped with a dash light. But it's easy to add. A small side marker light bulb will work. Stick to the automotive type bulbs though. Many others will not be durable enough to survive the vibration they will get on your tractor. If you don't want to drill the dash you could put the light on a bracket near the key switch or under the hood. My 1948 tractor already had an extra hole in the dash from a previous owner's start switch that bypassed the neutral interlock. I repaired the original start pushbutton and used the extra hole for my alternator light. Once you have a location for the light, simply run a #14 wire from Terminal #1 on the alternator to the light bulb, and from the other side of the bulb to a switched, 12 volt source. You can also put a 10 ohm wire wound ceramic resistor (Radio Shack® part No. 271-132) in parallel with the indicator light. This allows slightly more current to flow to the alternator field terminal and may help the alternator begin producing power at even lower RPM. This resistor does not affect the functionality of the indicator light. However, it will get warm. It's basically a little 10-watt heater, so put it in a location where it won't melt anything. Added bonus: If the dash light bulb fails this resistor will still allow field current to get to the alternator, so it will continue to charge. Terminal #2 This is the Remote Voltage Sensing Wire and it should be connected to the main accessory terminal where your ignition switch, light switch, and other accessories get their unswitched battery power. On the Ford tractors the best place is on the terminal block where the accessory side of the ammeter is connected. The remote sensing wire is supposed to sense system voltage so the alternator can regulate the proper voltage to your ignition and accessories. Most conversions show just a short jumper wire from Terminal #2 directly to the alternator output (BAT+ terminal). This is the third wire that I believe is missing from It may work OK that way, and it is certainly easier. However, if it would work correctly on every vehicle by wiring to BAT+ at the alternator, the Delco® engineers would have wired it internally and saved the trouble and expense of a separate external connection. Properly connecting the remote sensing wire, enables the alternator to regulate voltage to your accessories and more importantly to your ignition circuit. One difficulty with many 12 volt conversions is properly sizing the resistor to protect the coil. If the voltage sensing wire is jumpered at the alternator, it will lock down the alternator output and prevent it from compensating for other accessory loads. Actual accessory and ignition circuit voltage will be allowed to vary over a much wider range thta could cause hard-starting, no start, burnt coils, and other under and over-voltage related problems. The only way to guarantee maximum performance from your new alternator is to run a #14 wire from Terminal #2 and connect it as close as you can get to the main accessory terminal. Finally - If you are going to all the trouble to do a 12 volt conversion, you might want to consider removing the Ammeter. If you run a single wire from the solenoid directly to your junction block, you will remove two connections on the back of the ammeter that carry a lot of current. That gets rid of two potential problem spots. The 6 or 12 volt electrical system does work fine with the original Ammeter. Amps are Amps, the ammeter gauge does not care about voltage, so it will work ok. A voltmeter will fit in the same hole the ammeter came out of. The only wiring connection you need is a small #14 wire to a switched source. On these tractors the best place is the coil side of the ignition switch. Since a Voltmeter is not IN the main circuit between the alternator and battery, very little current goes through it. In my opinion, a Voltmeter gives a BETTER indication of the condition of your battery and charging system. When you first turn the key on, you get an immediate reading of battery voltage. A reading of 10 volts or less is considered dead, anything over 12 volts is at least a 50% charge and 12.6 volts is considered fully charged. While the engine is running the voltage should read between 13.5 and 14.5 volts if your charging system is working properly. For a 6 volt system, just divide those numbers by two. If you are interested, I have a page of general information about Automotive Batteries HERE |
