Similar thing happened to me a while back as I got back from Devon.The last 60 odd miles I had everything switched on and as I went to switch off on the drive the key wouldn't turn off and was a bit warm.Found out the nylon bit in the switch had melted from the current draw and the little plate that does the switching was going wherever it wanted.Didn't burn out anything but was getting there.The fuse box was melting.
I rebuilt the barrel holder with chemical metal,added loads of relays,and checked that the fire extinguisher has a chance of working.It's the nice 2a switch with the lighting switch incorporated that costs at least 50 squid to replace so I had to fix it.
I love electrickery.