Check that shitty fuse wire for the main fusebox feed, the main thick red wire from the fusebox to that battery has a black fuse link wire about 4 inches long (depending on what youve been led to believe an inch is ) theyre shit in my opinion, on moth my cabby and my orion ive cut them off cos they were all corroded and fraying, and put anline fuse holder with a 60amp fuse in, or u could get the fuseholder off a mk5 escort and use that, thats what im puttin my money on, losing an earth somewhere wouldnt cut the whole car out unless it was the main earth from the battery, check the terminals are tight aswell you would be surprised