Farmall A spark problem

Hi!
I just bought a nice looking Farmall mod A here in Norway, still wearing its original paint.
A few of these came over in the late '40s as a result of the Marshallplan, so these tractors are pretty rare here in Norway.
So.. To the problem:
The tractor was running good when parked outside (under some plastic) 2-3 years ago.
I tried to start it up today, but nothing happend. I checked,and it had no spark.
After checking wires, changing plugs and spark plug wires, cleaning the points, rotor and cap i get some spark, but not enough to even make a pop.
When connecting a test plug to it and turning the engine with the starter, i see a very weak spark that comes and goes.
It lookes like it is sparking maybe two turns,then misses one, and sparking again. Sometimes the spark will be all gone, and then suddenly it is there again.
Any ideas?

Sounds like the points could be corroded up, make sure you have voltage from the battery to the on/ off switch then to the coil then from coil to the points

The points look fine.
Not sure how to troubleshoot on this positive ground system, very confusing:)
The swich only has one wire on it, so i guess the swich only conects the wire to ground when activating?
When measuring between the "in" wire on the ignition housing and the ignition housing itself. Is there suppose to be conection all the time? Isn't the conection point supposed to be isolatet from the housing? I'm thinking I could have leakage to ground somewhere.

I should have asked do you have a magneto or distributor. Check and make sure there is no bare spots in the wire and check where the wire goes in the housing

H4 Magneto. Visually it lookes just fine, will take it apart to inspect now.

I was just down in the garage checking. As I said, I do not fully understand this reversed ground system.
When i disassemble the wire from the coil, and measure between ground and this wire I get a full conection.
Also the wire from the swich has full conection to ground when swich is turned off.
Is this right?

Being a mag setup the one wire to the switch is to ground out the mag to kill it, check you switch, disconnect it and see if you got fire to the plugs, a mag system doent use battery voltage it produces it own, so what ever you do don't connect a battery to the wire going to the mag or you will burn it up, you might need to file the points they could have a film on them from sitting

Ok, this make sense :)
But how about the coil? Is there suppose to be conection between the wire coming from the coil and ground?

Tried to disconect the wire just to eliminate the swich/wire beeing the problem, still no difference.
Point are good, already gone over them with a file.

Is there any way you can post a pic of the setup