MF4253 Charging system

BadMF

New User
Hello again. Ran into another issue I couldnt solve on my own, and since you guys were so helpful with my last question I figured Id come here once more... what Ive got is a charging system issue. The alternator was replaced by me and works as it should, battery is new and works and charges on my boat. However, the 14-15v from the alternator is not coming across on the battery terminals. Ive confirmed that the battery ground and alternator ground are good, but I dont have any continuity fr the alternator output to the battery positive post. The tractor does start and most electronics seem to work.

Ive Checked around a bit with the meter and made a strange discovery, at least strange to me. The output of the alternator seems to go to the starter solenoid on a small terminal separate from the rest of the equipment attached to the main positive post on the starter solenoid (where all the fusible links etc are attached) . I purchased a replacement solenoid and although the part numbers match, it is missing the small terminal that the alternator output is connected to on the old one. Part numbers match otherwise. Now, maybe this was dumb of me but I decided to connect me meter across the battery terminals, and then touch the alternator output wire to the main positive post Of the starter solenoid and sure enough the voltage across the battery went from 12.5 to 14.6 as if it were finally working. But I cant shake the feeling that the terminal it was connected to is there for a reason. Does bypassing it like that cause any problems? The tractor stills runs and starts if I disconnect that wire so I know it has nothing to do with the relay. I guess my question is can I just change out that connector to a ring and put it with the rest of the stuff on the main positive? Would that do any harm?
 
(quoted from post at 11:44:22 12/04/20) Hello again. Ran into another issue I couldnt solve on my own, and since you guys were so helpful with my last question I figured Id come here once more... what Ive got is a charging system issue. The alternator was replaced by me and works as it should, battery is new and works and charges on my boat. However, the 14-15v from the alternator is not coming across on the battery terminals. Ive confirmed that the battery ground and alternator ground are good, but I dont have any continuity fr the alternator output to the battery positive post. The tractor does start and most electronics seem to work.

Ive Checked around a bit with the meter and made a strange discovery, at least strange to me. The output of the alternator seems to go to the starter solenoid on a small terminal separate from the rest of the equipment attached to the main positive post on the starter solenoid (where all the fusible links etc are attached) . I purchased a replacement solenoid and although the part numbers match, it is missing the small terminal that the alternator output is connected to on the old one. Part numbers match otherwise. Now, maybe this was dumb of me but I decided to connect me meter across the battery terminals, and then touch the alternator output wire to the main positive post Of the starter solenoid and sure enough the voltage across the battery went from 12.5 to 14.6 as if it were finally working. But I cant shake the feeling that the terminal it was connected to is there for a reason. Does bypassing it like that cause any problems? The tractor stills runs and starts if I disconnect that wire so I know it has nothing to do with the relay. I guess my question is can I just change out that connector to a ring and put it with the rest of the stuff on the main positive? Would that do any harm?

Alternator output should go to the same terminal on the solenoid that the battery positive cable connects to. Or to the load side terminal of an ammeter in some cases.
 
I connected it and ran it but it seems like it never stops charging the battery... battery voltage was at 13.3 with tractor off after running it for a bit. Im wondering if this wire isnt the main output, it does seem a bit on the small side for something meant to carry a lot of current but I could be wrong... maybe its where the signal from the alternator to the no charge light in the cab terminates? Or would that be something that would be connected to a ground?
 
(quoted from post at 13:56:09 12/04/20) I connected it and ran it but it seems like it never stops charging the battery... battery voltage was at 13.3 with tractor off after running it for a bit. Im wondering if this wire isnt the main output, it does seem a bit on the small side for something meant to carry a lot of current but I could be wrong... maybe its where the signal from the alternator to the no charge light in the cab terminates? Or would that be something that would be connected to a ground?

The alternator output wire should be about a 10 gauge wire on most any alternator and should be connected to the largest insulated terminal on the alternator. Guess I better ask what brand alternator you have and how many wires go to it. It should be a MAGNETI MARELLI or a DENSO, by the parts book. Can you post a picture of it showing any wires connected to it? If your alternator needs to be excited to start charging, it is possible the wire to excite the alternator was hooked to the starter solenoid terminal that would be for resistor bypass on a gas engine. The excitation wire would be a smaller wire.

An alternator will normally show over 14 volts when charging, so you might see a 13.3 surface charge on the battery right after shutting it off.
 
There is the solenoid and the alternator, the blue wire on the solenoid is the one Im picking up 14.5 volts on. In the picture its connected to that small terminal that isnt on the new one... it is the MAGNETI that matches whats in the parts book, 70 amp I believe
 
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I will admit I am not familiar with the terminal locations and functions on the Magneti Marelli equipment so likely I'm not going to be any help to you. I am interpreting three terminals on the solenoid as the two studs and one spade terminal as in your picture. Looking at your solenoid picture I would say the spade terminal the blue wire is on would energize the solenoid to engage the starter. But if it has 14+ volts on it all the time as you say, and the starter isn't turning, that thought is wrong. I would have expected the wire on that terminal would only have power when the key is turned to engage the starter. Where is the wire to engage the starter and where does it connect?

I believe the output of your alternator is the wire which is connected to the B+ terminal. If you have an indicator light for charging, the small brown wire plugged into the alternator may go to that. I don't know about the black wire visible in the background. just my thoughts from your pictures. Hopefully ptfarmer, or someone familiar with your tractor's system, will be along and may be able to help you.
 

Yes, sorry, didnt realize it cropped the picture a bit but the spade that accepts the starter relay voltage is in the top right of the photo, the wire is connected and looks like a black 90 elbow in the pic. That one is for sure to engage the starter as unplugging it prevents starting. Youve already been tremendously helpful and I greatly appreciate your time...
 

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