Farmall M ammeter randomly spiking

[706man]

The belt seems pretty tight. Every time the hood is off I try to tighten it.

Right now, using drawing 5 that was posted here today, the system seems to be working. Other than the original problem of the ammeter pegging at 30. With the tractor off the battery is 13.7 volts and with it running is bounces around at 17, 18 and 19 volts. Is that good enough to say the alternator is working? If so, I am guessing I don't run the tractor enough to charge battery.
Thanks for the pictures and the guidance.
Now that it is most likely wired correctly I can order the new components and swap them out. Then wire the lights up.

 

[used red MN]

With the tractor off the battery is 13.7 volts and with it running is bounces around at 17, 18 and 19 volts.

What kind of meter are you using? The static voltage of a fully charged 12 volt battery is 12.7 volts. If you checked it right after you ran it and it was actually showing voltages between 17-19 volts it might be understandable because the voltage in the battery would be dropping to stabilize. The voltage on an alternator that working correctly should never go over 14.5 volts. Do you still have the points ignition on this tractor? If so the and you have a cheap digital meter the “electrical noise” from the points may be making it give erroneous readings. What does the ammeter do after running it 5 minutes at half throttle? If the battery had a sufficient charge to start the tractor unassisted it should show a higher charge for the first several minutes and then drop back once the charge in the battery builds. If it continually shows a high charge rate I would take the alternator to be tested and tell whoever is testing it you suspect it is over charging.

 

[Jim.ME]

Indications are the alternator is working; the internal regulator might be acting up.

The alternator is likely capable of 63 amps output, that was a common output so you should have a 60-0-60 range ammeter not a 30.

 

[706man]

I do still have the points in there. And was using a multimeter from my father in law who is an electrician. Had it set on 12v. I used the tractor today for a half hour doing some chores and all seemed fine. I will get the alt tested.

 

[used red MN]

I do still have the points in there. And was using a multimeter from my father in law who is an electrician. Had it set on 12v. I used the tractor today for a half hour doing some chores and all seemed fine. I will get the alt tested.

If it doesn’t seem to over charge per the ammeter all is probably good. If it does show 17-19 volts on the battery that is questionable. If the meter is a Fluke brand it should be good, otherwise it would be interesting to know if the one he loaned you was just a cheap knock around.

 

[Brownie450]

Believe I'd put a 40 Amp breaker on the L terminal of the meter
& then put all load wires on the remaining breaker terminal. Just
a little extra insurance.
Jim

 

[706man]

So referencing drawing 5 posted earlier, if I installed a 40 amp breaker, it would go somewhere between the "bat" from alt and the ammeter post that says "to headlight switch"? Which, if I am learning here, means the breaker would trip if the alt output is too much for gauge, everything, etc?

 

[Brownie450]

I usually put the breaker just off of the BATT terminal on the starter.
Since you have the ammeter easy to access, easier to do it there.
Jim

 

[Jim.ME]

So referencing drawing 5 posted earlier, if I installed a 40 amp breaker, it would go somewhere between the "bat" from alt and the ammeter post that says "to headlight switch"? Which, if I am learning here, means the breaker would trip if the alt output is too much for gauge, everything, etc?

You would make a short 10-gauge wire to go from the L (load) post of the ammeter to one of the breaker terminals. Everything currently shown on the L post would be moved to the other terminal of the breaker.

Yes, the breaker could trip if alternator output exceeds 40 amps for long.

 

[Jim Becker]

If I were to install such a breaker, I would attach only the lead from the alternator to one side of the breaker. I would leave all other load connections on the other side of the breaker or on the ammeter. This way, if the breaker opens, the failing alternator will be totally isolated. If done the other way, when the breaker opens the lights, gauges, etc. will be exposed to the uncontrolled voltage from the alternator.

 

[706man]

On the Bob M drawing with the circled 5 in upper left corner, the top terminal on his ammeter is the bat and bottom terminal is load, correct???
I just got my new ammeter and lightswitch and the center fuse and holder. I believe I have the front end wired right based on used-red's last post.
But verifying the ammeters posts will help me.
Remind me again the functionality of the fuse in the center? Assuming to protect the lights? And in Bob's "5" drawing, the fuse would probably be in the middle of his notation "to headlight switch". So, BAT side of AMMETER goes to fuse then to red terminal on headlight switch.
You can see I color coded the terminals on the light switch. From instructions I got for connecting light switch, the red terminal connects to one terminal on fuse, the blue headlight terminal goes to headlights. My rear taillight is just a standard headlight so i can figure how to wire that one.
Hopefully this will make it easier now that I can actually hook up the new parts. Thanks!

 

[Jim.ME]

If your ammeter was marked good. If not and an ammeter reads backwards, you just swap the wires from one post to the other and the reading will reverse. No harm, no foul.

I put the battery power on one post of the ammeter and all the other wires go on the other post (ignition, alternator, lights, etc.), as Bob's drawing shows; that way it reads what is actually going to the battery, not the battery and anything else that gets put on the ammeter's battery post. In Bob's drawing the fuse would be in the wire he shows going to the headlight switch, from the load terminal, not the battery terminal of the ammeter.