JD 4240 Charging sysm not working.

[Racer11]

The other day while bailing we discovered that the alternator was not charging like it should. Upon checking with a volt meter we discovered output was what the battery voltage was 12.4 volts. When shut the engine down the voltage test was the same,,,obviously nothing coming from the Alternator. We took a reading from two locations,,,,From the starter and the other from the high voltage stud on the alternator, all the same reading.

Off we go to the parts store and hooked up with a new alternator and installed it and the same problem existed. We took that alternator back off and installed it on a similar JD and it works fine at 14.4 Volt output,,,, now we know the alternator is good and proven to work.

My question for help is where,,,,else can we check the system that could cause this issue? Were scratching our bald greying heads at the moment...

Thanks

 

[Tx Jim]

Sounds as if the wire that is intended to excite the alternator has an open & isn't providing electricity to regulator when ign switch is turned on. Problem could be a break in the wire or bad connection at wiring bulkhead at firewall behind engine.

 

[Plantation Paul]

Field wire is not getting power. Should switch off and on with the key switch.

 

[Racer11]

Field wire is not getting power. Should switch off and on with the key switch.

Where is the field wire located,,,I assume it is the wire that excites the alternator..... There is a plug with two terminals on it that plugs in to the Alt. and we found one of those wires going to the plug and in bad shape. It was taped up and had been spliced together some time in the past.

Is that the field wire,,,,

Thanks Gentlemen

 

[jd110]

The 2 wire plug on top of the alternator contains the exciter wire. Terminal 2 (inside wire) should have 12 volts at all times. Terminal 1 (outside wire) should have power when key is in "on" position. This wire is a resistance wire and gets brittle and prone to breaking especially up front where the fan can cause it to move or vibrate. If you have no power to that outer terminal with key on, alternator will not charge.

 

[Plantation Paul]

It has been a long time, but I think it has an "F" on the housing?

The same alternator will bolt up on my 1980 Z28, FYI. Delco alternators were on most JDs until the 60 series. They went to Nippondenso then.

 

[Plantation Paul]

 

[Racer11]

Well,,,,from the info here my son n law and myself found that the resistance wire was the problem. We found it to be all broken and rotted etc etc all along the wiring harness clear up to the bulkhead. I did not know it was a resistance wire until I just read what jd110 just posted,,,I thought it was some kind of a problem with a short causing the decay but now I know. I also discovered that the outer terminal was without power with the key on.

It is obvious that we need a new wire harness with the wire broken brittle and broken all the way almost to the bulk head,,,,$$$

I want to thank y'all for helping solve this problem,,we were getting stumped to a point with this deal.

 

[Tx Jim]

If you want to replace wiring harness rather than splicing in a resistance wire you could check with Agri-services for a price on wiring harness. Wire Harness, Tractor Parts, Harness Repair, Alternator Conversion, Braided Wire