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Heres how I wire a GM 10SI Alternator on gas tractors using a coil ignition system, if its on a Diesel, they can be excited by use of a Normally Open Oil Pressure Switch with a hot wire feeding its input and its output used to excite the alternator via the 10 ohm current limiting resistor (see below) when she sees oil pressure and remember, it requires NEGATIVE GROUND !!!!! ! The big rear main alternator output terminal goes to the wire that used to be connected to the BAT terminal on the Voltage Regulator or Cutout Relay. HOWEVER if that wire wasnt already upgraded, when I convert from a Genny to an Alternator, I replace that wire with a 10 Gauge and it runs from the alternators main output up to the LOAD (NOT to battery/starter) side of the ammeter. I also replace/use 10 Gauge from the ammeters other SUPPLY terminal to the battery/starter. The little side number 2F Voltage Sense Terminal gets connected (use a short 14 jumper wire) right up to to and with the big main output terminal mentioned above. For the little 1R side Excitation Terminal, run a 16 or so gauge wire from the ignition switches IGN (which is HOT ONLY when ignition is turned on) terminal and in series with it place a 10 ohm 5 watt current limiting protection resistor (dont really need that much wattage power rating, but they are heavy duty built and easy to wire). Then in the rare event a gas tractor continues to run cuz of alternator backfeed when the ignition is switched OFF, I add in series a 5 amp 50 PIV minimum Diode. The diode must be wired with negative cathode end to the alternator and positive anode end to the switch. Again, the ratings are not that exact but about any diode over a few amps and 50 volts or so works. Dont forget to change the battery to negative ground (if its not Negative already) and if a gas tractor the coil needs to be wired so the negative goes to ground via the distributor points and the positive gets power from the ignition switch and you have to reverse ammeter leads also if your changing polarities from Positive to Negative. Good luck Ol John T in Indiana
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