MF 135 battery draining

[HoosierMuscle]

Hey all. This tractor has a new battery and new Voltage regulator (105289 from here). The alternator that was on it has been rebuilt (Delco 1100828). The battery will
drain down overnight. I recharged the battery and have 12.75 volts but the voltage will immediately start to drop until I unplug the F terminal on the alternator. This wire
goes to the F terminal on the VR. I measure between the wire on the VR F terminal and the negative lead of the battery and see 12.75 volts. I then measure between the
F terminal on the alternator and the ground of the alternator and only see 6 ohms. So, Im confused on if I have an issue on my alternator or VR side. Should the F
terminal of the alternator be grounded? Should the F terminal on the VR be putting out 12.75 volts? Im guessing I have an issue on my VR. All grounds are clean with
no resistance on the VR. Ive attached a wiring diagram that pretty well matches my tractor.

 

[J.Wondergem]

If this were me, I'd replace the alternator with one with the regulator built in.

 

[hearnc843]

I would start with replacing the regulator. It's hard to tell if you have the wiring right from the photos, but assuming everything follows the wiring chart correctly, it could just be a bad alternator, but that is more expensive to fix. I think regulators are around $20

Should be getting 14V also. If you don't see a spike in voltage after starting it, it could be a bad regulator. Also old fuses are another cheap fix. If you have the old style glass fuses, upgrade to the new double spade automotive style fuses. The old glass fuses go bad and will develop high resistance and only let a few watts/volts through. Happened to me.

 

[HoosierMuscle]

Well, I caved and put a 1 wire alternator on it. Was less than
$100 from OReilly which is about half of what I paid to rebuild
the 3 wire and get a new voltage regulator. For anyone hunting, I
used a Wilson 90-01-3125 and it bolted up perfectly. Ive only
got a 12 ga wire ran to battery and will upsize that soon.