I am in the process of converting my Allis Chalmers D-17 to an altenator but I can't fine much information on how to wire it. I bought a single wire altenator for it but not sure what I else I need. It is a positive ground 12V right now.

First, good to see you posting my friend. Second, I wish I could help, but a positive ground alternator is something I have not heard of. Seems like it would have to be wired internally for that.

I've never seen a 12V positive ground system but if it is you should be able to put a negative ground coil on it and run. Hook up the battery as a negative ground. Run a wire from alternator to positive post or solenoid. You can even try hooking up your existing coil as a negative ground.

not sure if this can help

In thinking about positive ground, it is important to NOT overthink it. The chassis/frame/body is positive. If you want to use standard accessories in such a system, then wire accordingly. If the case of the accessory is negative grounded, then it will have to be actually insulated from the positive ground chassis. A coil is an inductor. An Electrical field can be built up either way. WHen the field is interupted, it collapses, resulting in inductive 'kick' flowing in the opposite direction. You should be able to use the coil. Just keep in mind which way your system assumes current flow. That is the key.

Good thoughts DP! I take it that the Alice is a 9V Positive ground right now correct?

Why do you want to go 12V? Cranking speed or some such?

An ammeter indicates current flow. Current flows through the instrument. The needle will indicate direction of flow in most automotive applications. The connections will be same polarity to same polarity..as in think of the ammeter as a piece of wire. The ammeter is usually connected so that it treats current flow towards the battery as positive and current flow from the battery as negative. I am unsure if the ammeters in the old cars are able to handle the large currents directly or if they are picking up the flow an an inductive manner. Most test meters that read more than a ampere do so through inductive measures.
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A voltmeter indicates potential. It is far easier to properly and safely connect. One simply connects the instrument with respects to proper polarity on any fuse protected circuit.

Another way to think of it, an ammeter is a series connected device, a voltmeter is a parallel connected device.

If the new alternater is designed for a 12v negative ground system, it will be difficult to use it. The case is the negative ground the wire goes to the positive battery teminal. To use it, the case would have to be electrically isolated from the chassis. The alternator case would have to connect to the negative battery cable. The wire from the alternater would hook to the tractor chassis. It would be much better to get a one wire positive ground alternater, if such a thing exists. An alternater shop sould be able to wire one for positive ground. The other alternative is to convert the whole thing to negative ground, but that may introduce issues with attachments. It would also require isolating or replacing many of the elctrical devices in the tractor. The harness could likely be kept. Wire doesn't care about current direction, just amount of current flow. Some ends on the harness would likely have to be replaced or modified. Simplest solution, get your one wire alternater in positive ground configuration. An alternater is an AC device. Internally, current flows both ways. It is rectified into DC and then regulated to maintain a voltage. The shop would likely only have to change a couple of internal connections.

I have converted several 6V postive ground cars to 12V negative ground. The only problem was that the ammeter worked backwards, easily fixed by swapping wires side to side. The gas guage won't work in some cases. 6V radio and clock is a no go. New 12V bulbs don't care. The 6V starter doesn't care. A new 12V coil and everyone is happy!

How many bulbs and junk is he going to have to worry about on an Alice Chalmers?

Thanks for all the info. As far as I can tell, the tractor was always a 12V system or was already converted from a 6V long before I got it. The gen doesn't work anymore and would cost a fortune to rebuild.
Do I have to change the points? I saw something once on "Two Guys Garage", but I couldn't find anything about that episode on their website.

Points, no problem, just a contact swhitch.

Maybe condensor and coil, but try what you have first. If they don't overheat and cut out, you're good. You should wire in a dropping resistor to the coil/points if there isn't one already.

I got looking at my old Ford and it has a ceramic resistor on it.