On the Xtype its almost always bad battery cables, most notably the positive has too much resistance from the alternator to the battery. If you use a digitsal volt ohm meter and measure the voltage at the battery posts, and then at the postive cable on the back of the alternator you'll find there's usually more than .10 volts or more difference between the 2 and you need a new postive cable. Oh, that light meens there not the correct voltage to the battery