550G alternator swap

[TomBall]

I have a John Deere 550G with a Prestolite alternator. I want to change it and have found many Motorolla style ones that cross over to the John Deere part number. Are they truly interchangeable from the Prestolite ones?

 

[Tinkerer]

I don't know about the interchange compatibility. But why not a new aftermarket one ?
Or rebuild the one you have if it is possible.

 

[TomBall]

The aftermarket ones also dont look the same in the back where the wires hook on. I think there are wiring instructions that must be included when you buy one. They all cross over to the John Deere part number. I can get a good deal on the Motorola style . Yes, I can have mine rebuilt, but it probably cost as much or more than replacing it.

 

[Tinkerer]

You may end up and have to take a chance and buy the Motorola one. Provided it is returnable if it isn't what you want.
Have you tried contacting one of the vendors with the Motorola and ask them about the wire connections.
Maybe someone will chime in here that has done or tried the swap.

 

[TomBall]

I will study the wiring on the prestolite one to see what they are responsible for. With alternators with internal regulators, I would think they should be compatible. The aftermarket ones also look a little different in back even though the are shown to cross over to the John Deere number, so I guess it doesn't matter which one I try. I was just hoping someone already ran in to this.

 

[Orest Anhel]

Motorola alternators on JD350 and 450 machines use an external regulator and are somewhat expensive to replace. Very common to install a Delco 1 wire alternator with internal voltage regulation

 

[TomBall]

Well, I bought the Motorolla style and installed it after some problem searching. When I took it out of the box I was totally confused with the wiring decal on the back. After some thought I figured the tag was put on upside down. I contacted the manufacturers tech hotline and to my surprise they could not answer my wiring questions. Next I contacted company headquarters without much help either. They gave me a phone number of a long time rebuilder to see if he could help. After calling him and discussing the problems he told me where all the wires went even though the alternator did not have a warning light post. And yes the tag was upside down. After trying to put the original pulley on the new alternator I discovered the shaft was bigger and I had to bore the pulley out on my lathe. It is now on and charging. So my findings are that the alternator that directly crossed over to the John Deere part number was not usable without modifications. Anyone trying this same route better have lots of patience and some machining capabilities. It kind of defeated the whole concept of direct replacement.

 

[Tinkerer]

Thanks for the update, Tom.
There aren't many of us that could do the lathe work it required.

 

[DMiller]

I do!!
There are other ways, like asking for the correct pulley when pick up the new alternator, usually cheaper than modifying a old one.