406 Trip Computer conversion

[bennyalford]

Hi folks,
I have a D9 model 406 (late 99) which came with the basic multifunction display (time and date). I have access to a crashed 2001 406 with the trip computer function, from which I've swapped over the display unit and the wiper stalk (with trip computer button). So far the new display shows the time and date, and if any systems are faulty (e.g. 'ABS FAULT'). So far so good.
The temperature appears as '--', so I need to add an external temperature sensor. I believe these go in the passenger side wing mirror, however is it likely that the harness connection is there for this already (mirrors removed from donor car so I can't inspect this). If so, what connection is it?
Also, the trip computer function doesn't seem to work - nothing changes on the display when I press the button on the wiper stalk. I assume there is a separate trip computer module that needs adding. Can someone let me know where this is located, and again if any harness changes may be necessary?
Thanks,
Benny Alford