The spare wire I used wasn't part of any loom or even an add on. It was actually internal and went under the ply floor with the rest of the speaker wires. So if you've got the opportunity then I guess it can go under the floor? TBH I didn't really know what it was and just left it when I refurbed the interior last year.
I also had a new loom last year, now all I need is a new gearbox!
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