Tn75a alternator issues

[DirtyDusty]

I have a Tn75a that started having the battery light come in at lower idling speeds. If I revel up over 2000rpm it would go off. Then it stopped going off and would run the battery down. I checked the voltage at the alternator, and would only have battery voltage. I then took the alternator to a shop and they went through it, and said it checked out fine.
I installed the alternator and cranked it up, light went off for a few seconds then came back on, still not putting out any voltage. Could there be another issue, like the voltage regulator, causing the alternator not to put out voltage?

 

[Jerry/MT]

Does it have a separate voltage regulator? if so that could be the problem. Make sure that your battery ground is making good contact at the terminal and the chasis. Are the battery terminals clean?

 

[DirtyDusty]

It has the internal voltage regulator. Cables are clean and tight.

 

[DwayneB]

If the belt isn't loose probably the alternator.

 

[RickB]

Typical alternator failure scenario.

 

[DirtyDusty]

Took the alternator back to the shop that rebuilt it. He put it in the machine while I watched. Voltage fluctuated a little, so he put a new voltage regulator on and tested it again. Everything looked good, so I brought it back and put it on. Still get no out put with it on. The alternator shop said the little spade that the single wire slid in, should have some voltage to it, because that is what triggers it to charge. The battery has 12.3VDC on it and that is the same voltage I get on the exciter wire too. Battery light stil stays on too. Anybody got any ideas?

 

[Harry in Ky]

If it charges on the test bench it should charge on the tractor. Seems to me there should be an AC tap to power the tach. Does that work? If the exciter signal is there and the tach works, I'd be suspicious of the battery circuit. I would clip a jumper wire from the alternator output terminal straight to the battery positive post and see what that changes.

 

[DirtyDusty]

I tested the exciter wire with the key turned on, but not running. No voltage, so I jumped it to the positive side of the battery and the alternator started working. Couldn稚 see any wires broken going to the dash, and the battery light stays on, unless I jump it out.

Anyone have a wiring diagram for a Tn75a? If I leave it jumped out while running, will I overcharge the battery?
Also, the tach is working, too.

 

[DirtyDusty]

Is there another sensor that is between the battery light, on the dash, and the alternator?

 

[Walt H]

The exciter wire needs to have power to it when the switch or key is on. If there is no voltage present with switch on, there will be no output from the alternator. Check your switch.