Couple of quick updates from a few weeks ago.
Cruise control all sorted.
Behind the glovebox on the passenger side is where the brake switches reside (yes, I know that sounds odd, but it's true...).

The white one on the left is the normal brake switch. The red one on the right is the 'redundant brake' switch which runs the cruise control.

(Pics taken from the breaker that picked the switch up from)
On later models, it's a single switch with 4 contacts, rather than 2 separate switches.
All fitted (5 minute job) and cruise now all working
Next job was the external temp sensor;

(Take at least 20^C off that number to get the correct value!

)
It lives in the bottom of the nearside wing mirror. I assumed it was guff because of this;

(water getting in)
So the breaker also yielded a replacement. Door card needs to come off in order to do it, so all in about 20 mins.
From that, to this;
Oh...
One step forward, one step back, then
I sodded about for a bit checking it was nothing obvious. You can swap the connector around. I found if it was flipped 180^C, I got a reading from the new sensor (albeit one that was hopelessly wrong

)
Plugging the old one back in as a comparison showed that when the plug was put in upside down, it doubled the temperature reading, which was interesting/surprising.
I'll get round to looking at this again some day, when I swap the interior probably.