TO30 Alternator

I will be replacing my Alternator but am confused because one of the wires coming out the 2 prong clip, runs to the Ignition Switch and connects to the ACC pole. I do not have any accessories on the tractor- no lights, no horn, etc.
1.) Why is a wire ran from the Alt to the ACC pole on Ignition Switch and do I need to do that?
2.) Type or Model # of Alternator to buy.

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You would need a contact development diagam for the switch to know for sure but IF ACC is hot when ignition is on it maybe provides power to excite the alternator for charging.
You could test it with a voltmeter to see for sure.

Start it up, check with voltmeter to verify it charging, then pull the ACC wire and see if it stops charging.
Other than that, I dunno.

Do let us know how you get on with it.

The earlier alternators 10SI type have three wires. The single terminal hooks to the battery usually through an ammeter. The terminals marked 1 & 2 are thus. 12 volts to #2 for reference, switched 12 volt from in your case ACC to #1 to excite the charging circuit. Very necessary. Newer alternators usually have just one wire and do not require being excited. Some just need to be turning a certain rpm to start charging.

I forgot to mention there should be a bulb or a 10 ohm resistor in the line from ACC to #1 terminal.

So if I were to get a newer Alternator like you mentioned that self excites, do I still need that resistor?

With a 3 wire Delco alternator pin #1 requires a momentary voltage to get it charging, then internal diodes in the alternator take over and supply operating current to the regulator.

If there is no isolation on pin 1, when the ignition switch is turned off the diodes will continue to supply power to pin 1, back to the switch, and to the coil and the engine will not shut down.

There are several methods of isolation. A resistor or idiot light limits current below that required to operate the ignition system. A diode blocks current one way so it will not flow back to the switch.

Normally an accessory terminal is on when switch is on, but when off it is isolated from the ignition post so current can not flow back to the ignition. Thus a resistor, diode, or light is not necessary to prevent run on but may help to prevent surges that could damage the alternator.

My self,if the #1 connection is already there I would get a 3 wire Delco alternator, like for an early 80?s GM vehicle. ?One wire? alternators are usually old original 3 wire units that have been modified.

?Start it up, check with voltmeter to verify it charging, then pull the ACC wire and see if it stops charging. ?
Even if you remove the ACC wire the alternator will continue charging. A Delco 10SI internal regulated alternator only needs a momentary voltage at pin 1 to get it to charging. Once charging you can disconnect the wire and it will continue to charge as long as the engine is running. Some installations actually use a momentary switch to send a start up to the alternator and then release the switch. Only problem is to remember to do it each time you start the engine.

The picture below is the Alternator and Excite Wire. Do you know where I can find that particular Excite Wire set up as the internal nodes inside the clip are corroded.

The 2 Alternator Connector should be available at any auto parts store NAPA 787105 would be one example