Converted H to 12V and ignition switch acts up

Good evening. I just recently converted our 1950 Farmall H from 6 to 12V. I have followed the instructions from this site as well as had my converted M next to it to follow with and feel I have it wired correctly with the alternator putting out 13+ volts. The issue I am having is the original kill switch was working correctly (on/Off) before the conversion and then after converting the system, it will not kill the engine when pushed in (checked with voltmeter and it has continuity in both states). Thinking this was just a fluke, I replaced the switch with a new. I checked the new switch before installing and it would loose continuity when pushed in like it should. After installing the new switch I started the tractor and the switch worked just like it should. We took the tractor for a drive for about 25 min and when returning to the shop, the switch would not kill the engine again (I pulled the coil wire to kill it). The rest of that day the switch would not shut the engine down. The next day, we moved the tractor again and by habit pushed the switch in to shut off and it worked. Tried it half a dozen more times and worked just as it should. I have tried it since and it seems to still be working correctly. Any thoughts?

I should add this tractor is new to us, so know very little history.
For the conversion I installed the Delco 10Si alt and rewired with diode.
New 12V coil and ballast resistor.
New Ammeter.
Lights are currently not hooked up.
Thanks in advance.

I would put an amp meter in the ignition circuit to see how much it draws. if more than 4, maby 4.5 amps, the system is drawing too much amps. Possibly a failing 6v coil or wrong ballast resistor or?
It could also be a bad diode (shorted). If it keeps doing it I would pull the plug on the alternator to see if it stops when you can't stop it with the switch. Jim

Sounds like the diode is wired up backward.

Try swapping the connections at the diode - good chance the ign switch will now kill the engine properly.

Thanks for the suggestions. I will look into those. The diode was factory installed on wiring lead (which does not mean much these days), but if it was backwards, wouldn't it do this every time not just intermittently?

When it does work it probably means you haven't run the engine fast enough to excite the alternator. Once the alternator is excited it backfeeds the ignition system.

I have my excite wired through an oil pressure switch. Works just fine.

Did you add a diode to the system. If not it back feeds voltage with the battery connection to the alternator and even with the switch off it continues to run and you can't turn off the tractor.

Yes I did add the diode to the system. I purchased a 2 wire plug with the diode already installed. I am wondering after reading several responses if it was installed backwards from the supplier. I will swap connections over the weekend and see if this helps. Thank all of you for the help so far.

The old switch may have failed. New switches from some third world sweat shop may not function reliably either. Intermittent problems suck, but if it's currently working, there's "no problem".

Met a fellow ages ago wearing a T-shirt that had printed in small text over the pocket: "it was working when I left". Seems a firm in Colorado had an employee who would bandaid problems rather than really fix them. Callbacks galore. That was the line he always gave the boss. They got him a bunch of T-shirts as a 'going away' present. Some of the other employees wanted and got one as well. Been a number of times since I first saw it that I wanted one too.

Thanks for all the help guys, I appreciate it. I will start off with checking the diode direction and operation and then take it from there. Like "WellWorn" stated the intermittent problems suck and right now there is "no problem" but I am sure it will return. Thanks again and I will let you know what I find. Have a great weekend.

If you were to unhook the wire at switch going to the coil when it was running, switch shut off, and would not stop, you would determine immediately if switch was at fault or you were feeding back from alternator. In other words, if it keeps on running with wire at switch unhooked you know feed back was problem. If it now shuts off, switch is problem.

suggested Pulling the Plug on the alternator. Kinda the same thing. Jim

I missed that apparently.