I've recently gone through two alternators on my wifes 99 XK8 in a span of about 2 months. In both cases a diode has gotten very hot and the alternator no longer charges. I would like to know if there is any common problem with the XK8 that can cause this diode death. These alternators are a real pain to replace.

 

Have your battery checked first. If that is OK, check your battery to alternator cables for broken strands or corrosion. Also check the high current fuses and associated connections in the the trunk.