pugs seem Very suseptable to bad earthing problems.. try cleaning the battery terminals, and basically make all earthing points (main one should be on top of the gearbox) are shiny and make good contact..

i made up a new earth strap for mine just to make sure too .lol


just another thought... any signs that the altenator might be on the way out??

what sorta set up is it running? standard proper managment? or 8v managment with a distributor? or is it on aftermarket stuff