[Darren69]

I've just had a quick look at the wiring schematic for my S4 which will be similar to the 620. That 30A fuse is called the General fuse but its fed directly from the battery + on one side and the ignition relay on the other side, so check the igintion relay is all good. Its also fed by the reg rec which is behind the 40A main fuse so check the charging is within the limits Gazza said, it could be overcharging. It dioes't look like there is much else on a direct feed from that fuse (The ignition key switch itself.) Those would be the things I would check all connections on first.