Fat 50 johnson seahorse 50 hp

[Seahorse50]

I have 1959 fat 50 model v4s-11.
My issue is no spark, I'm wondering when the key is
On should I have 12v going to the lead wire on the side
of the distributor?

[Joe Reeves]

NO, you DO NOT want battery voltage going to that distributor.

Those old V4 50hp models used a belt driven magneto. The ignition is self contained.

Battery voltage would destroy it!

[Seahorse50]

Ok thank you, glad I asked first.
So leaves me wondering what is that wire for?
It runs from the magneto down to the side of the distributor
Where it bolts on and continues to the harness plug.
I don't see this wire any where on my wire diagram.

And what would be things to check for a no spark issue?

[Joe Reeves]

1 - Ok thank you, glad I asked first. So leaves me wondering what is that wire for? It runs from the magneto down to the side of the distributor where it bolts on and continues to the harness plug. I don't see this wire any where on my wire diagram.

2 - And what would be things to check for a no spark issue?

1 = That wire (top to bottom on the magneto itself) runs from the dual point sets to the hidden coil.

1a = That wire continuing on into the wiring harness leads to one of the "M" (magneto) terminals of the ignition switch. Another black wire runs from the remaining "M" terminal of the ignition switch to ground.

When the key is ON... There is no continuity to ground = Ignition exists.
When the key is OFF.. There is continuity to ground = Ignition is eliminated.

2 = Dirty points, points set wrong, condensers shorted, coil cracked and faulty, rotor shorted out to driving shaft, wrong rotor installed.

NOTE.... The rotor is similar to the rotor used on the automotive ignition BUT they are not interchangeable.

The automotive rotor has a straight screwdriver type end to its metal lever.

The magneto rotor has a wider hook like effect to the end of its metal lever.

[Seahorse50]

Ok thanks, so if I understand this correctly if
I thought it may be a faulty ignition switch
I could unhook the m terminal.
And I then would have spark if it's shorting in
The switch? Otherwise Ide likely need to check ohms
With a meter to test other components.

Of course cleaning points, checking gaps & timing aswell.

[Joe Reeves]

If I understand correctly, I could unhook the black wire at the "M" terminal that leads to the magneto... then I would have spark if it's shorting in the switch?

Yes, BUT only IF everything is as it should be within the magneto.

HINT... If one knows how to time the engine, it's a lot easier to simply remove the timing belt so that the magneto pulley can be spun by hand.