I'm installing a GM 10SI 3 wire alternator on my case round nose 300 series tractor and would like to know if anyone has used this alternator and how to wire it? I have read that a charge light (idiot light) is used on the #2 wire sensing (spade plug) and want to know if a voltmeter could be used in place of the light? I already have the alternator mounted and just need to wire it. I also have a 12SI 1 wire GM marine alternator but I don't think the motor will turn fast enough to turn it on so it will charge or will it I just don't know.

The main thing to remember when wiring to terminal 1 is when the alternator isn't charging the terminal is grounded, and when it is charging the terminal has 12 volts output. But it takes about 5 volts to make the regulator turn on to start charging. That's why a bulb or diode works good, or a momentary switch could also be used once the tractor is running.

This is a pic of the 10si wiring that a guy name Bob used to post over on Tractor Talk forum.

I've done 3 of these 10si conversions on my own tractors. I buy a universal 4 terminal ignition switch and connect the sensing wire to the accessory terminal. That eliminates the need for a diode or resistance in that circuit. The accessory terminal is hot when the ignition switch is on and open when the ignition switch is turned off, there is no path for feedback and run-on.

Joe

Here is a diagram that shows the more correct location for sense wire .If you are going to the trouble why do do it the more correct way like the GM factory did.

http://bob_skelly.home.comcast.net/~bob_skelly/alternator_conversion/wiring_alternator1.html

The #2 "sense" terminal has NOTHING to do with a diode or indicator lamp. It is simply jumpered to the alternator's large output stud, or for more accurate battery voltage sending, connected to the battery cable at the starter switch or solenoid. It can remain powered up at all times.

The #1 terminal is the "excite" terminal, and that is the one that gets connected to the "load" side of the ignition switch, though and indicator lamp or a diode.

I think that Delco alternator works better with a diode to excite it than a lite. Go over to the Farmall board and look up a diagram for any Farmall letter series in the archives and follow it. The same diagram will work on the letter series Case tractors, too. I've used that diagram for a Farmall Super H and a DC Case & both alternators work just fine. The advantage of that Delco is that it has an internal regulator. (My $.02 worth. jal-SD)

Roger, go to the articles link on the left side of this page. Then go to the link, step by step 12v conversion. It gives you the step by step instructions and there is also a wiring diagram. The volt meter will not take place of the light but you can replace the light with a diode. I can not remember off hand what the correct size is for the diode. I have wired many 3wire alt. it is not difficult at all. Dennis