1987 MF 375 not charging batteries

[Overkill338]

When I take the connector off the alternator, all three prongs show 14 volts. When I put the connector back on the alternator and test the back if the spade connectors, they show 12 volts while idling and 11 when I throttle up. Both batteries are down to 11 volts.

The tach stopped working a couple days ago as well. This tractor has just under 2100 hours.

Please give me an idea where to go!

Thanks

 

[denchen]

It`s difficult to answer your problem not being there, but I would start by taking the single wire off, and with a volt meter or bulb, check that when you turn the key on you get the battery power there, and it goes to zero when you turn off the key. You say the tacho stopped a few days ago, so I`m thinking a dodgy fuse or a loose connection. It seems your alternator is OK but something is not telling it to charge.

 

[Overkill338]

It`s difficult to answer your problem not being there, but I would start by taking the single wire off, and with a volt meter or bulb, check that when you turn the key on you get the battery power there, and it goes to zero when you turn off the key. You say the tacho stopped a few days ago, so I`m thinking a dodgy fuse or a loose connection. It seems your alternator is OK but something is not telling it to charge.

Thanks, I will try that shortly. There was a blown 10 amp fuse I forgot to mention behind the dash, but I replaced it first thing yesterday and it changed nothing. Only 3 fuses in the box and no labels of what they are. This isn't a cab tractor. The 10 amp was in the position closest to the engine.

By the way if you're talking about the single wire that's on a stud. It had 7 volts on it when the tractor is running.

 

[WranglerX]

First thing I would do is take alternator to automotive electrical shop and have it professionally tested, if its good then yes problem is in electricals of tractor...

If alternator has external regulator it could also be failing regulator...

 

[Overkill338]

First thing I would do is take alternator to automotive electrical shop and have it professionally tested, if its good then yes problem is in electricals of tractor...

If alternator has external regulator it could also be failing regulator...

They are internally regulated.

 

[Overkill338]

It`s difficult to answer your problem not being there, but I would start by taking the single wire off, and with a volt meter or bulb, check that when you turn the key on you get the battery power there, and it goes to zero when you turn off the key. You say the tacho stopped a few days ago, so I`m thinking a dodgy fuse or a loose connection. It seems your alternator is OK but something is not telling it to charge.

Key on the single terminal has 0.25 volts. Key off is 0.10 volts.

This terminal correct?

 

[denchen]

With that single wire off, is there a full 12v or what every your battery is at, ``at the wire`, when the key is on, and zero when the key is off.

 

[denchen]

Mind you don`t ground that wire when the key is on, or it will blow a fuse.

 

[Overkill338]

With that single wire off, is there a full 12v or what every your battery is at, ``at the wire`, when the key is on, and zero when the key is off.

I tested the terminal not the wire. Is that what you meant.

 

[denchen]

Test the wire, you need your battery voltage there when you turn on the key. This wire `tells` the alternator when the battery is full.