Farmall H not starting and 12 volt conversion

I have a 1944 Farmall H that was restored about 5 years ago, but now am having difficulty starting it. I decided to convert it to 12 volt. It was positive ground, so I put in a new 12 volt battery, ran a cable from the negative post to the ground at the starter. Ran a cable from the positive post to the starter button, where there I also connected a wire to the new 60 amp ammeter. The other wire from the starter post went to the starter. Where the wire from the starter post connected at the ammeter, I also connected the wire for the new ignition switch, as well as a wire connected to a 20 amp fuse that ran to a new 4 position light switch. The other post on the ammeter just has a wire running to the new alternator. From the other connection on the ignition switch, I have a wire running to the positive side of a new 12 volt coil with internal resistor. A wire from the negative post of the new coil runs to the distributor. Replaced the distributor cap and ran all new spark plug wires and put in new spark plugs. When I turned on the ignition switch, my test light shows power to the starter post and also at the new ignition switch, the alternator and the coil. When I try to crank, I can see spark at the points where the distributor cap and rotor come off. I do have a spark plug analyzer that shows that there is a spark (although very small and hardly noticeable) to the plugs from the distributor to the plugs. Tractor still won't start. I took off the carburetor and everything seems fine.

The other issue I'm running into is the rear taillight will not work. I installed new wiring to the headlights and those work fine. I have a wire running from the ammeter to the 4 position light switch with a fuse, and then a wire running from the light switch to the headlights. Again, they work fine. I then have a wire that runs from the light switch to the rear light. My test light shows that this connection is good. I also tested where the wire attaches to the back side of the tail light fixture - test light comes on. I took the old housing inside apart and the test light comes on where the inside housing attaches to the post inside. But the unit itself still wouldn't light. I ended up buying a new housing....same problem. Test light comes on outside the unit, inside the unit and also where the light bulb makes the connection to the housing wire itself....I tried several bulbs.

Any ideas?

For the taillight problem, it sounds like the taillight housing isn't connected to a good ground.

How is the housing mounted to the tractor?

Normally taillights are grounded through their mounting bolts, so whatever your housing bolts to has to be connected to ground for electricity to flow and the lamp to light up.

It sounds like electricity is getting to the taillight, to the bulb, and to the housing, but it's not getting past the housing to ground.

I'd run a temporary separate wire from a clean metal part of the housing to the negative battery post and see if it will light up then.

so it didnt start with 6v going to 12v isnt the answer take a plug out and hook the wire to it and then make sure the plug is grounded. If no spark work backwards till you find the problem. Have you ran a compression check maybe the valves are stuck ,set bad its worth a look

It's been really tough trying to figure this thing out. It was running until about a month ago, but didn't seem like it was running on all cylinders. Pulled off one of the plugs and I could see a piece of brass in there - it turns out last year the fuel metering nozzle came off of the carb at the brass nut holding it in, blew up into the manifold and into the head. Pulled the head off and got the piece of brass out and looked like it didn't do any damage. I put a new gasket on, reinstalled head and everything ran fine. Compression was good. Spark was good. Ran it for about 20 minutes with no problem. Came back out an hour later so I could check for leaks around the head and to re-torque if needed. Tractor wouldn't start. A couple days later I changed it over from 6v to 12v and it still wouldn't start. Test light was on/off as it should showing the distributor points opening up. Then it seemed like it wanted to start for about 5 seconds and then died. After all that cranking, I could tell that the starter brushes were going bad. Have that pulled off and having a shop rebuild it as we speak, so my options are limited at the moment until I get that back. Thanks for the advice!

Thanks for the advice! You would have thought I would have realized that! Tail light is simply mounted with a bolt attached to a clamp that is mounted through one of the bolts for the transmission cover/operator base. Both painted. I'll give that a try. Couldn't for the life of me figure that out!

May not be the problem... but, is there enough gas in the tank? I've cranked, cranked, cussed, and took apart things just to learn I was out of gas!

So, the point we are at now is after it quit running after running 20 min. after you put the head back on? This is when you decided to replace a bunch of ignition components and convert it to 12 volts correct? If so you could have accidentally changed the order of the plug wires in the cap or the plugs wires getting them out of proper order. I believe if everything is correctly timed as it was from the factory number 1 spark plug wire terminal is marked on the cap (IH brand for sure maybe others). So as viewed from the back (seat side) it should be at the 1 o'clock position in the cap and the and firing order (1342)and distributor rotation are clockwise. You say the spark seems week that sounds like a condenser or coil issue if the points contacts are good and the gap is correct. What does your "spark plug analyzer" look like? It may be for modern ignitions with higher spark voltage. Just use a good plug(take the one out of your running lawn mower if need be then you know it works)and hook the coil output wire to it and ground it to the block. On your 12v conversion the one side of the ammeter should ONLY have the power lead you run from the battery side of the start switch. The alternator feed, ignition and lights all should connect to the other ammeter terminal. None of this has anything to do with the engine not running just how the ammeter will work after you have it running. It may take swapping all the wires to opposite sides of the ammeter if once you get it running and the charge discharge is backwards. Sorry for the novel. Good luck.

What make/model of alternator you using? And forgot the most important thing WELCOME to YT!