JD MT 12 V Conversion

phil(va)

Well-known Member
Any recommendations for best way to convert the MT to 12 volts? Is there a full kit available anywhere? This site lists Alternator and Bracket separately. Anyone sell full kit with instructions?
 
Take a look at the photos below of one way to convert a 6v system to a 12v system.

This method will work on the MT as well as the Model 40.

The photo below displays the wiring for the ammeter, exciter switch, and ignition switch.

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The exciter switch is simply a push button on "Audie" our Model 40S.

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You might consider installing either a push button or toggle switch in the hole on the MT dash panel.

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The photo below shows the wiring for the starter switch.

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The photo below displays the wiring for the alternator.

a182982.jpg" width="650"


Hope this helps.
 
Please explain the advantage/benefit of using a diode rather than an exciter switch?

Which wire is the diode attached/connected?

Can you recommend a diode part number and supplier?
 
You are the only one on the site that I have seen with an exciter button. You just hook between the ignition and the excite terminal on the alternator with a diode to prevent back feed.

I think it is a IN4001 diode.
 
You really don't need to spend all that money on a conversion kit. Any GM vehicle from the 80's will have the alt you need. Three wire Delco available rebuilt at most any auto parts store for less than $50. You can get a universal top alternator arm pretty cheap there too.

There are quite a few ways to wire it. Use James pic as a guide. Search 12v conversion here and you'll find the diode way.

My M is wired old school the way a local mechanic did it some thirty years ago. 1&2 (plug) wires are crimped together and run to a GM oil pressure switch I installed just below the alternator. From there it runs to the big stud on the back of the alternator. That makes it a one wire alt to the back. It excites when oil pressure rises and is removed from the circuit when it drops at shutdown. This isn't really proper but it's worked good for me all these years.
 
Thanks for the additional information on using a diode to prevent back feed.

The diode prevents back feed to which electrical part in the system?

Take a look at the photos below of "BW" our Model 40T without an exciter switch.

Wire from the ignition switch to the alternator 1 excite terminal.

a183023.jpg" width="650"


The diode (warning light) between the ignition and the alternator excite terminal.

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The wire from the ignition switch to the alternator 1 excite terminal.

a183025.jpg" width="650"


This was the wiring "set up" when we bought the tractor.

Thanks again for the information.
 
James;
The diode just prevents battery drain from the alt plug to what it's hooked to. It isn't proper but I use an oil pressure switch for the same purpose.
 
Thanks for additional information on using the diode to prevent battery drain.

Even if the method on your tractor may not be considered proper by some, as the old saying goes, "there's more than one way to skin a cat".
 
The blue wire goes from the ignition switch to the ballast resistor.

The blue wire then goes from the ballast resister to the <big>+</big> positive terminal on the coil.

a183041.jpg" width="650"


Hope this helps.
 

The wiring in these pictures is for show
right?
The finished product doesn't look like this
does it?
 
I have my Farmall H wired with an oil pressure switch too. If it shows charge, you know it has oil pressure at start-up.
 
These photos were taken to "document" the electrical work done on these two Model 40 tractors.

They come in really handy if/when another tractor gets rewired.

They may also come in handy when answering questions relating to the electrical system on an M, MT, or 40.

Yes, this is the finished product.
 
I took that normally open momentary 'exciter switch" path when I replaced the original generator on the family's 95 round back.

The generator had a hard time keeping up with lighting load anyway and when it developed faults to ground in the armature it waw time! We put the alternator from a 76 (I think) Chevy Pickup in and wired it with a dash light. The idea of keeping the dash light was it helped make sure the key was off & the battery would not be dead next day. Most times the alternator would come to life and do his job without help but occasionally it would (for some reason) be reluctant to come to life without throttling up to full governed speed.

Some times even if you went to full speed it would refuse. That was possibly too low a wattage bulb in the dashboard but not liking to wind up a cold engine and not wanting to take more time to wire in the diode, I put that exciter switch in. I could then give the alternator a tickle with a quick tap of that tiny little black button. The alternator would wake up & bury the ammeter at little more than a dead idle. It was cheap, simple easy and never went bad.

Never missed the generator after that day!
 

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