I have seen a big white long plug at the back behind the radio, it has a pink/green wire. This loom appears to drop down towards the fuse box. Is this the otter switch wire (there isn't another here) which if I earth it the rad fans will wire up?
I seem to remember reading the wire is present as this white connector as you mention. Connecting it to ground should trigger the fans, maybe someone else can confirm before you test it.
Are you sure it is Pink/green? I suspect it is Green/pink in which case being up near the radio it is wiring built into the loom for air conditioning and as you suspect is there to turn on the fans for A/C.