Sten

I have been enlisted to help with a 1972 Targa that's had an engine bay fire - the loom has melted as far as the torque tube. I've managed to strip enough to splice new wiring in, but I can't identify three wires - they appear to be run in a separate loom, but don't appear on the wiring diagram I've got. The three wires are Red, Brown/White rings and Red/Black trace. The three are all heavier cable than the rest of the loom, anyone give me a clue?