12 v system charging system

I have put a new alternator on my to20, checked the wiring per diagram. Ammeter never records any thing, the battery reads 12.9 volts not running, tractor starts fine, but the voltmeter goes to 0 while tractor is running with leads attached in the same place. The whole system was replaced before I got it, and a keyed switch was used. The only wiring diagram I can find does not have a key switch. Really need some help.

Okay, I am not as familiar with the Ferguson wiring lay out
as I am with Farmalls but I am sure I can help you out.
First I need info about the alternator one wire or 3
wire? Is it a Delco 10si or other? Did you buy it new if
so where? You wired it per a diagram can you show me
the diagram by a link or photo. If it is a link, if you do
not know how to post a link tell me if post in Modern or
Classic and I will explain how. Tell me if the key switch
is off-on-start or only ignition off-on. Look at the
..generic.. diagram I am attaching. The two
connections off the ammeter shown as heavier lines
should be 10 gauge wires. The one on the left
connection should go to the end of the positive battery
cable opposite end from the battery wherever that
connects. The one on the right should go to the
alternator stud terminal. The battery voltage should be
tested at the battery posts, if I ask what is the voltage
when you do xyz that is what I mean, voltage at the
battery terminals. If I want a voltage check somewhere
else I will instruct you where to test. I assume by volt
meter you are referring to a test meter if you are
adding a volt meter to the tractor let me know about
that.
Edit to add: Where I reference the linked diagram above I am suggesting to compare your wiring to this. I believe diagrams supplied with some one wire alternators do not show connections through the ammeter. In my opinion this setup would require using a volt meter gauge instead of the ammeter. If you are considering this beware a volt meter wires in very different from an ammeter.
Generic 6 to 12 volt conversion diagram adding alt.


This post was edited by used red MN on 11/20/2023 at 06:36 am.

Zero charge at idle Possible small pulley on tractor (driver). When engine revs up over the alternator 1200 charges.
Does alternator have an internal voltage regulator ,or is it an external mounting of voltage regulator ?

If you are using a digital volt meter you may be getting false readings when the tractor is running. If
you have access to an analog voltmeter give it a try to verify interference isn't confusing the digital
meter. I have seen it happen many times.

When you say with the leads attached in the same place, where exactly are the leads connected?

It is very possible for you to get the results you mention depending on where the leads are connected.

You need to provide more info, no one here can see your tractor. The parts book shows a keyed ignition switch for the TO20. Do you mean the switch was changed to one with a start position and a solenoid added so that the starter is engaged by the key switch, not the gear shift lever as original?

As has been asked, what alternator? Internal or external regulator? Is the pulley width correct for the original belt width? What is the diameter of the pulley?

What wiring diagram did you use?

Can you make and post a sketch of the wiring as you have it currently connected?

It sounds like your tractor has an ammeter and you are using a handheld voltmeter for testing. What wires are connected to which terminal of the ammeter? Where are you attaching the leads for your test meter to the tractor?

Ya Jim no response. I can only believe that the diagram
I posted gave him what he needed. I know rustred has
mentioned that some new one wire alternators show
the main output terminal wiring going directly to the
positive battery cable connection. Which would
obviously eliminate any reading by an ammeter.

The new ones that wire the alternator directly to the battery source likely use a voltmeter or trigger a warning or a check engine light if the alternator is not charging.

Well I am sure you know rustred he said, I do not need
a gauge or light telling me the alternator is working
every second. I can see his point to a degree,
alternators are fairly reliable.