Farmall H 12V conversion

Hello, I apoligize in advance for the lengthy first post but here it goes. I am converting an "H" to 12 volts for my aunt. I read a lot of posts on here about the conversion but have some questions. I plan to use an Optima gel battery and will have to build a new battery box. It looks like width and height of the original box are OK but not the length. It appears it needs to be about 1 1/2" longer. Is there room to accomodate a slightly larger (longer) battery box? I will use a diode instead of the light in the alternator circuit. What amp rating does the diode need to have? I read these tractors were originally positive ground systems and the ammeter will read backwards which is easily corrected. How do you get the starter rotation correct? Some of the info I see is for the "M". Are the "M" and "H" electrical systems the same or close enough that the "M" info also applies? Will the standard pully on a typical alternator spin it fast enough to charge effectivly? I will take pictures and try to post them when finished. Thanks, Kevin
 
Find Bob Melville conversion diagram and select your tractor to convert to 12 volt.Most of your questions will be answered. There is enough room for larger battery box. The pulley size shouldn't be an issue. The starter will still turn the correct way.
 
Here is Bob M's wiring diagram I sort of "re-worked" to my application of a Hitachi alternator on my H. No need to worry about the starter, just wire to this diagram and all should be fine. If you use a Hitachi alternator the pulley is supplied, but requires you add a washer between pulley halves to accomodate the belt. When mounting the alternator take off the generator mounting bracket that bolts to the engine and flip it upside down. Use some 3/8 all-thread to mount the alternator to the bracket, and the whole assembly should fit under the stock hood. PLEASE, do not cut the hood!!! Hope this helps.
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If it has a magneto you will need to supply 12v to the excite (L) circuit from bat +/ I like a oil pressure sensing switch (NAPA) that is on with pressure. THis eliminates the diode, and all is well. The mag is not connected to any thing other than its kill button. Jim
 
the starter dont care if its pos. or neg. ground it still turns the same way reguardless.
and yes this info dont care if its applied to the m,h,or any of the other models.
 
A standard pulley will work fine, starter does not care about polarity. The Hitachi alternator comes with a pulley that works and fits nicely.
 

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