Heard of it once before - 1990 GT that fried it's rear wiring loom last year.
From what I can recall (it's all a little hazy) his rear loom frayed around the bootlid catch area and shorted out on the chassis. He needed all the boot plastics, carpets, loom, and rear seat. Lucky the fuel tank didn't catch I guess.
It'll take you to look at it in the light. Have a few beers and chill tonight. Tackle it in the morning mate.