460 - main fuses?

My battery went flat the other day and got one of my neighbours to help me out today, we started out with regular car-car-cable and I got the instrument-lamps to activate, not enough current to turn the start-motor though. We increased the rpm at the working car and suddenly everything went flat, no lamps no nothing. My neighbour was very persistant about trying to tow it, (not recommended i've heard, it's that just a rumor??), anyway, no action in any sense, no lamps, no nothing, even on towing in 1:st gear. So.. Is the computer dead? The relay broken or is there just a fuse somewhere that's been blown to pieces? Just found one, attached beside the generator, it seems abit far fetched that it's the one, and it's quite sealed as well. Thankful for any hints. Gee, if my daughter knew what her fiddeling with the lamps in the backseat can lead to... Cheers,

Power 

Check the main engine earthing cable at the gearbox. Paul.