Hook up a 12v bulb or test light inline on your positive(red) battery cable. The brighter it glows the more current is being drawn (a short). Try to half-split the circuit by disconnecting connectors/wires halfway between the battery and motor until the bulb dims alot or goes out. A dimmed or outened bulb indicates no current flow/no short.
Try the starter wire, alternator wire, keyswitch wire, on board charger etc until the bulb dims or goes out and you wll be close to the culprit my friend.
Tom