I went and tidied up all my junk, then reversed the van into the garage (the wiring runs down the driver's side) to make working on the van easier. I've crawled around underneath it, and pulled bits of wire around to discover where it is. It's looking like it'll be a pain to pull wire through the stock tubing, but I'm going to give it a go... I've cut the wire at the rear, and soldered the new wire to it. I did start trying to pull it through, but I was obviously trying to pull it too far, so I'll try cutting a hole nearer the engine bay and pulling from there. At least I can now work in the garage in the evenings, rather than having to drop the van out of the garage to do anything.
I cleared up a bunch of the leaves out the front of the house - at least until the green waste bin was full. And the pick up is the week after next, so here's hoping that the storms are done with - the sun came out in the afternoon and cheered everything up, Tilly and I went for a walk.