My MF service manual said that ignition points are set up for 5 amperes of break current. Break current is when the points open and the coil dumps into the spark plug.
Assuming no inductance is part of that number, you take 12v (12.75 or 14 when the engine is running at moderate rpm's and the gen/alt is putting out) divided by 5 amperes and you have your wiring dc resistance measured in ohms; actual measurable resistance with an ohmmeter, from the battery to ground through all the ignition operating components.
Doesn't matter where it is unless you have a bypass circuit in your ign switch which bypasses an external resistor (usually half the circuit resistance) to put full voltage across the coil to aid in getting a hot spark for starting......since the starter pulls the battery voltage down while cranking and you need all the help you can get....and since farm tractors may sit out for long periods in the weather and all, the battery charge could be pretty low. (I think Ford, for one, had it in their cars.)
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