(800) 853-2651
SHOP NOW

Voltage Regulator Question

Yesterday's Tractor Forums
J

JBMac

Member
Good Morning,

I posted this on the MF forum and didn"t get much response. I know there are other great minds besides Massey Ferguson owners! My 175 diesel with factory alternator and external voltage regulator is not charging. I have totally redone the wiring according to Big Dean"s wiring diagram. I am trying to figure out if my problem is the regulator or alternator. According to the diagram, the regulator is labeled, from left to right,F-2-3-4. Can anyone suggest the best way to trouble shoot the system? The oil pressure switch is working and sending 12V to the regulator. Thanks in advance for all of the assistance.
 
You may have a blown diode, you may need to pull the alternator and regulator and have them checked at your local shop where they repair generators, starters and alternators. Hal
 
Howdy JBMac. Hope this writing finds you well and in good spirits. I would think you could put a volt meter across the alternator and read the output, likewise across the regulator. I don't understand why you say the pressure switch is sending 12 volts to the regulator. Seems to me it ought to be the other way around. The switch should be receiving 12 volts. Just a thought. Merry Christmas to you and yours. Take care.................RW
 
I believe on the diesels, the oil pressure switch engages the charging system. Kinda like a run indication. I read the post on the massey forum but as I originally had a genny regulator setup and switched out, I never took the time to learn how it worked.

Wish I could be more help,

Aaron
 
To determine if the alternator is GOOD, "full-field" it (for a short period of time) by pulling the connector off of the back, and jumpering the terminal labeled "F" to the large output stud on the back of the alternator. This will make it charge at it's max output.

Before doing the jumper thing, check the voltage at the large output stud. Without the alternator charging, it will be around 12.5 Volts. When you install the jumper, if the alternator is working, the output voltage will quickly come up to 16 to 18 Volts, or even more.

Use an ANALOG meter, as many digital meters are "freaked out" by the "noisy" electriacl systems on these old machines.
 
Right Aaron, but there's more. The oil pressure switch. "excites" the alternator on those Masseys. The external regulated alternator found on the 100 series is totally different than a "3 wire" alternator. While you'll find a FIELD terminal and a SENSE terminal on the alternator, they don't use both. The pressure switch gets 12V from the regulator and once it senses oil pressure (your "run indicator") the switch sends power to the "F" (field) terminal of the alternator. That excites te alternator. This wiring scheme causes the alternator to charge as soon as the engine is running instead of having a cut in point determined by RPMs like a 3-wire alternator. There is no "sense wire" used.

Also, the pressure switch sends 12V to the fuel gauge so that the fuel guage is powered only when the engine is running.

Years ago I spent a week chasing a NO CHARGE on a 135 Massey thinking I had a bad regulator or alternator or wiring, only to find a bad PRESSURE SWITCH. Last thing in the world I suspected was something to do with the oil pressure gauge.
 
JB, Believe it or not, my MF175 had a 30amp fuse in the Bat wire on the Alt. Looked OEM. It was in the harness at about the front of the engine. Check for this as it would surely make a no charge situation. I just twisted the wires together on mine eliminating the fuse. I'll see if I can post a pic later.

And do as the other said, full field the alt, this will check the Alt without having to take it in for testing.
 
Hey Poor,

Thanks to you and everyone for the help. Take a look at the diagram I used, I think it may be different than what you are saying above. In no way am I saying Big Dean's diagram is wrong, he's certainly an expert, but maybe there's more than one way to skin this cat. I noticed that the harness I got off of fleebay didn't want to hook things up the way the diagram showed so I modified it. What d'ya think?
Untitled URL Link
 
Following this line of thought, it is possible then for this fella to have a bad pressure switch. If he does indeed have 12v going to the field of the alternator, it should charge. Being an externally regulated alternator and having the field energized, it should produce around 44volts. Correct? Hold on, I am going to look for a wiring diagram...

Aaron
 
View


I won't say the wires are hooked up at the same place as this diagram, but electricaly looks just like mine.
 
Aaron,

If you look at the diagram on my post below, the way I wired it the switch is fed by the + side of the ammeter. After it runs for a few seconds, it sends 12V to the #2 terminal, verified by my tester. The F terminal always reads 0V, making me think the reg is no good. When I jump 12V to the F terminal on the alternator, it's output on the big stud remains 12.5V, making me think the alternator is also suspect. I don't know what to think! Any input from your diagram would be appreciated, my manual must be older than my tractor, it only shows the generator setup.
 
Unless you guys are trying to keep them original? Why not use a 1 wire chevy style. Hook 1 10 guage wire to starter or battery and be done..Around $50.00 for a 1 wire alt. and all the wiring problems are solved, My mf20 industrial and my drag cars have been this way for years.
 
(quoted from post at 18:31:17 12/18/07) Unless you guys are trying to keep them original? Why not use a 1 wire chevy style. Hook 1 10 guage wire to starter or battery and be done..Around $50.00 for a 1 wire alt. and all the wiring problems are solved, My mf20 industrial and my drag cars have been this way for years.
Click to expand...

On a MF175 , at least on mine, the tach is run off the back of the alt. I have never seen a 10si drilled for the tach.

If the alt will charge when full fielded, I would bet on a bad regulator. I still would check for that fuse. I working on posting pics of mine.
 
You must log in or register to reply here.
Yesterday's Tractor Forums
Buy Tractor Parts Here Buy Tractor Manuals Here

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Copyright © 1997-2025 Yesterday's Tractor Co.

All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.

Yesterday's Tractors - Antique Tractor Headquarters
Website Accessibility Policy

Back
Top