John Deere 4600 Alternator Failure

glcaines · Jul 12, 2022

I have a 2000 John Deere 4600 tractor. While using the tractor, I smelled a strong odor of burning insulation and the charge light came on and the tachometer went dead. I disconnected all of the wires from the alternator and checked the output. It was dead - no output. I replaced the alternator with a new Romaine Electric 40-amp alternator. Now, the charge light is extinguished and the alternator is charging the battery. However, the tachometer doesn't work correctly. When the engine is idling it reads ~750 RPM. At very high RPM it reads ~800 RPM. It does respond to increases in RPM, but only slightly and very slowly. Any ideas? Faulty new alternator?

glcaines · Jul 13, 2022

I measured the output from the P terminal on the alternator and it was zero, no pulses. No wonder the tachometer didn't work. I removed it from the tractor. The vendor is giving me my money back, but now I am in a quandary. I don't want to spend the money for a very expensive genuine JD supplied part. The least expensive alternator from a JD dealer I've found was ~$400.00. Other vendors sell replacement alternators for my JD 4600 from $50.00 to $80.00 that are supposedly compatible. Who knows? Has anyone had experience with a particular model replacement alternator that functioned properly when feeding the tachometer?

K5lwq · Jul 13, 2022

Could you take your old alternator to a rebuilt shop? That is always my preferred solution to starter and alternator problems.

Roadworthy · Jul 14, 2022

I concur with K5lwq - get the alternator repaired by a local shop. If it's not repairable the shop can suggest a proper replacement and should even stand by you if it's not compatible when received.

glcaines · Jul 14, 2022

I took the advice and took the alternator to a repair shop. They told me that they should have it repaired by tomorrow. This same shop previously repaired the starter for my Mercedes Unimog so I know they do good work for reasonable prices. Thanks for the suggestion.