update on the farmall H

hey guys just an update on what is becoming more of a parts expedition than a refurbish. Started tear down a few weeks back and decided that I am going to work on the motor first and work my way back because fortunately besides the rear main it is not leaking and I am not equipped to split it yet so I am going to to an in frame rebuild and the body work. I am currently trying to work out the 12v conversion I am going to get a brillman kit and wiring harness but I do not know if I can keep my H4 magneto that I just rebuilt. I drew out what I think the wireing should look like. My question is the hot wire that goes to the coil can I use it as the hot wire for ignition coil that comes on the brillman harness to the magneto or will I need to create a ground for it? I really do not know a whole lot about 6 to 12 v conversions except that I know i have to change bulbs and ballast resistors on swithces and what not. Is there any one running a 12v conversion with an H4 Magneto?

Also I would like to add I am trying to build a stone boat/ fun puller I know I will be out powered by the others in my area for the local fair. I am also still looking for antique pull club near Fredericksburg va.

I've got 2 tractors converted to 12 volt alternators with H4 mags on them. If I remember correctly just skip the wire that would go to the ignition. The other wire goes back to the amp gauge and you don't need to worry about a diode or idiot light. Both of mine are one wire conversions. Hopefully someone else will verify that since I'm not near mine to refresh my memory for wiring.

There is one on there from the previous owner I was just going off of what I saw. Anything helps and I welcome the advise.

I put a TEE in the line that goes to the pressure guage. A oil pressure switch is wired always hot to send power to the alternator terminal if it is required to be excited. Any time you have more than 15 psi oil pressure, the switch is closed. This is on a Hitachi conversion. Put the pressure switch just behind the guage, It looks factory that way.
Switch polarity on your amp guage if doing the 6-12 volt switch.

Beagle

All's well except the kill switch to the mag. The mag is completely separate from all electricity. So in place of the location you have the wire to the mag from the ignition switch you need to erase that entire dangling thing from the drawing. The ignition switch grounds the mag when pushed in, no power there at all, and cannot be. In place of that (and the light as well) you can use a NAPA oil pressure switch that closes when it has oil pressure. It will have 2 terminals. attach one terminal to the ammeter as shown in your diagram, and the other to the #1 terminal on the alt. When the engine starts, the oil pressure comes up and the alt turns on. There is no need for a light there with a Mag. When the engine stops (because the mag is grounded through the ignition kill button as it is now) the oil pressure goes to zero and the alt stops charging. Jim

Here is an old YT post that shows you what to do so you do not need to have a switch to energize the alternator. It uses the engine oil pressure to close the circuit to energize the alternator ..excite.. circuit. It shows a Mitsubishi alternator but the wiring diagram they show is laid out like a 10si. I have not looked at an H for a while but I think if you got an 1/8 in. brass pipe tee with females on the straight through an a male out the side your pressure switch could mount in behind the side rail pointing down and the oil line could come out the top. This just avoids placing the T up by the gauge using compression fittings as they show it done.
Old YT post

That Brillman kit is pretty spendy. In the 1st link is a YT alternator bracket kit. The just go to a parts store and get an alternator for a 74 Chevy pickup with no A/C, should be about $40. Just to let you know and maybe you checked into this. The rear main is two half moon pieces of felt. To get the the seal in without the tractor split is quite a trick but it can be done.
YT alternator brackets

YT Farmall H rear main seal

You can use your H4 mag just fine. It makes its own electricity, and DOES NOT require any juice from the battery. Needs to be left alone, and it works independently.
Sounds like the kit and harness you are getting is for use of a distributor with a 12v coil included. The 12v coil you are getting is for replacement of the 6v coil used with a distributor. Since you are not using a distributor, you do not need and can discard the 12v coil. The H4 mag will need to retain the coil that it currently has and do not change it out.
That only leaves the matter of the kill switch for the mag. That just needs to be one wire ran through a switch to be grounded out when off. Not grounded (and NO juice) when switch is on. How you accomplish this, is up to you. But that's all it needs to make the H4 mag work.

P.S. I'm guessing that a 12v conversion kit and harness is only available for a distributor set up, and the same thing is all that is available for a mag set up. But, ... if you haven't purchased it yet, you might inquire if this stuff is indeed made for use of mag. But even if so, it's really not going to change much on what you are already getting. Not getting or paying for the not needed 12v coil would be the big thing. The only difference with the harness would perhaps be some length variance on one wire and possible an extra switch.