There are two relays for the heated front screen (right and left) as shown by the symbols on the cover of the engine bay fuse box and confirmed by
I found this in the manual: "The BeCM also receives a Heated Rear Window
(HRW) request signal from the HEVAC ECU in the
form of a momentary completion of an earth path
when either the manual HRW switch is depressed or
the programmed demist switch is depressed. When
the BeCM receives the request, it energises an
internal relay and supplies a 12 V supply to the HRW
element via fuse 12"
Sort of answers my question. Pity it's not external it would have been easy to change.
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