Battery not charging

MF202 w/ 134 Continental.
Found an issue I failed to look into some months back when I got it the tractor. After a fuel issue which was simple enough to fix, checked to see it was charging...it wasn't. All wires were connected where they should be. NOTE: The tractor still had the old generator installed. Pulled generator//regulator & installed alternator (charge output + FLD)//regulator from a 68' Dodge bus on the property (what was available); ran output to pos battery w/ FLD to regulator then out to the ignition. No charge.
Disconnected regulator then jumped the field//ignition connections...voltage varies but reaches up to 16+ volts. This seemed to say the old regulator was shot. Got a replacement (damn Autozone wanted 48$ for an exact regulator match...nearly 10x what RockAuto asks)...so got a generic solid-state from a local auto parts store for 13$ (2 terminal reg). Had to fashion up new connection ends but it STILL wont charge.

Once again d/c'd regulator and jumped the connections and got the 16-ish volts from before. This tells me the alternator IS putting out but am puzzled as to why I'm getting lower voltage reads with the regulator connected and tractor running ...than I do when its off.

Readings: 12.5 w/ engine off ---- 12.3-4 w/engine running & regulator connected (RPM unknown but the ear says 1500+ when tested) ---- 13.5-16+ w/ engine running & regulator bypassed.

EDIT: Not sure if this has anything to do with it but the alternator was D U S T Y inside...the bus has sat for over 20 years. I shook out as much dust as I could...though neglected to take the air hose to it to finish the job before installing it.

Sounds like you have the older Mopar alternator with the mechanical regulator and single Field terminal on the alternator. I suspect it may have sticky or worn brushes / corroded slip rings, as connecting full 12V to the field wire should give a steady 16+ volts.

Chrysler is about the only alternator that allows you to check / clean / replace the brushes without opening the alternator. Just remove the little screw at the brush holder and pull it out. one goes straight in from the rear, the other from the side. Pull the brushes out, clean and inspect them for wear, replace if necessary. Polish the slip rings bright using a pencil eraser on them while spinning the rotor.

Make sure the power to the regulator is full 12V, (not taken from an ignition coil after a ballast resistor). Make sure the regular has a clean ground, as it will not control voltage if not well grounded at the base.

Attached are wiring diagrams for early mechanical regulator and later solid state regulator alternators with double field terminals.
Mopar alternator wiring.

Rereading your post and see another possible reason for a no charge with the regulator connected.

If your replacement regulator was intended for a Mopar alternator with dual field terminals, it will not work on the older alternators with a single field terminal.

Reason being that the old mechanical regulator fed power to the alt field terminal.

The later mopar solid state regulator grounded one alternator field terminal, while the other alternator field terminal was fed 12V from switched power.

In effect, the old mechanical regulator was a type B system (internally grounded field)

The 1970 and newer Mopar alternator with factory solid state regulator was a type A system( (externally grounded field.)

The late type solid state regulator and early single field terminal alternator will not work with each other.

In answer to your first reply: After I get home tomorrow I'll check the alternator brushes. Given how much dust had collected on the outside (and no doubt inside) I wouldn't be surprised if something is sticking. Looking it up it is an OEM style alternator I have...the round skinny kind with LOTS of vent slits. When voltage was being checked, it was at the battery terminals.

To the second: Come to think of it that regulator does seem to closely resemble what I recall seeing on the firewall of a 79' Chrysler Cordoba also at hand. As for the regulator that was paired with the offending alternator it [i:8bb194bca2]looks[/i:8bb194bca2] like the cover could come off but lacks the typical 2 screws on either side. Though if what you say about the alternator is the case there could be nothing wrong with the regulator.

Will find out tomorrow.

If you get in there and find the brushes appear to be "worn out" as in so short they won't make contact, or completely gone, down to the spring... Don't waste your money and time replacing them. This is a sign of a shorted stator. New brushes won't fix it, least they never have every time I've tried it.

Once again d/c'd regulator and jumped the connections and got the 16-ish volts from before. This tells me the alternator IS putting out but am puzzled as to why I'm getting lower voltage reads with the regulator connected and tractor running ...than I do when its off.

If you mean you full-fielded the alternator and got 16+ volts; it is normal to have voltage spike on a full field test. The amperage should have ramped up too. You don't prove the regulator is good with a full field test, you determine if the amperage is sufficient from the alternator. Amperage should be 10% of rated output. By the way full field tests should be quick lasting no more than 10-15 seconds or you risk damage to the alternator.
You have not proven the alternator is putting out sufficiently unless you measure amperage. Or an old trick is to turn on all electrical accessories and run the engine at 2,000 RPM and make sure voltage doesn't drop below 13.2 volts. Gerard

What other electrical equipment? Have none...and the Cyclop-ian head light (1 side is missing entirely) isn't even hooked up. Sadly I don't have a portal ammeter to check with and what currently passes for instrumentation are rusty faced w/ broken glass. Tach is missing the cable anyway and was meant to connect to the removed gen set. Someone appears to have half/welded the instrument panel into place so will end up mounting a small 3-cluster on the right side below the steering wheel, opposite my bass-ackward forward/reverse select lever.

Since the replacement regulator doesn't appear it would work I put the old one back on and made sure all was snug and contacts made.
Was going to start by checking the brushes. Sadly couldn't see a removable cover to get to them. (BTW what I have is a Remy). Then noticed a connection on the back labeled GRND. It appeared it was meant to have a wire connected and got me wondering, but the screw refused loosening and appeared secured to the alt body. Rigged a wire to the block anyway and was going to retest by manually grounding. Voltage quickly rose to 13.3 then slowly rose to just over 14.2 and would vary by only 1/10V +/- and stayed good even when I ceased making the ground contact. Rechecked again after turning tractor off then back on...voltage good.

Appears to have been little more than a failure of Charging 101: MAKE SURE all connections solid. So either the regulator didn't get a proper ground before or my fidgeting with the GRND screw on the alt did it.

I will however keep in mind whats been said here regarding charging tests if the need arises again (whether on the tractor or any other vehicle).

Glad you got it going without a lot of work or cost.
If it has a Delco alternator, all the advice I gave is not going to be of any use. I was assuming the Dodge bus had a Mopar 60 or 110 amp alternator.

If it has a Delco alternator, it was added by the bus builder or a previous owner.