There is no master fuse for the +8 of that vintage. with the electrics completely dead (ignition, lights, horn etc.) I would first check the 'red key' isolating switch which should be behind the drivers seat on the kick board in front of the rear axle. Then check the battery and connections to the battery, then the terminal on the starter motor where the thick red wire from the battery connects to a terminal, and here the feed wires are connected that feed power to the fuse box.
Mike Smith
