390T alternator not charging Fuel, temperature & rev cou

Hi,

My friends Ferguson 390T is not charging. Belt condition was good, clean and tight!
12.29 Volts ignition off.
12.16 Volts Engine running.

I don't know too much about alternators, but with the 'engine off', I connected a voltmeter to each of the 3 terminals on the alternator which are under a connector.
Only one of those terminals are normally connected with a small wire - the smallest terminal of the three. At the small terminal that is connected no voltage reading - 0 Volts. However, battery voltage was present at the other two unused terminals. This was with the engine off - I didnt test it while it was running at those terminals as the connector should be connected.

Battery voltage also present at the large wire which I presume is the output feed.

Same voltage readings at alternator or battery.

Not sure if I was going the right way about testing it or not so please help. Is it possible to test/replace diode pack separetely?



Also the rev counter, fuel guage, and temperature guage are not working. The owner says these 3 problems occured at the same time. Not sure when it stopped charging as there is no warning light for that! Battery is still strong enough to start engine.... for now!!!

Rev counter is reading 5,000 revs with the engine on or off. Other guages are reading Empty and Cold! No loose wires or bad connections noticed around the back of the dash panel, or temperature sender unit.

Any advice please?

not for sure if this helps but on my 390 if the belt slips the guages won't work. as far as the alt. i think tkat the little 1 is the exiciter wire and with the key on it should have voltage. if you get it to charge i think the other problems will go away. hope this gives you some hope.

I also remember something like if the oil pressure guage reads above some amount it will excite the alternator and allow it to charge. I could be completely off on this one, but just a thought thrown out on the table. One thing you can try is to start the tractor, then disconnect the batter and meter around for voltage.

Hello,

I don't know 390 in particular. But it sounds that very likely the problem lies with the ignition switch, or oil pressure switch. I don't know which one of these the 390 has.

If the ignition switch has 0, 1, therm, start positions(like a car would), then the problem lies with the ignition switch. If the switch has only 0, therm, start, then it has the oil pressure switch, and a problem associated with it. The problem could also be with the wiring, so once you figure out what you have, it's best to check how far the power goes with a multimeter.