Re: what did you do to your motor bike today?
The size of the conductor inside a spark plug wire does not need to be very big at all. All it needs to do is carry high voltage between the ignition coil and spark plug boot. Spark plug wires are also heavily insulated for both durability as well as containing the high voltage adequately, and the thin conductor also allows the wire to bend and wrap around engine blocks and obstacles easily.
FWIW, a single strand of copper wire unwound from the welding lead you used would get the job done very well....but you would need to insulate it...a whole 'nother story here.
There is hardly any amperage involved to fire a spark plug.
Large conductor wire such as what you used from a welding lead is designed for high amperage as well as voltage. Definitely overkill indeed, but no harm done and will still work just fine.
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