Hi Nick,
Thanks for the advice!
Unfortunately the addition of the air con makes things a bit more
complicated ;-(
I believe that there is a different type of termperature sensor (thermistor
as opposed to a simple switch) which feeds to a control box. This in turn
decides whether to run the two fans wired in series (slow) or parallel
(fast) using the relays I found.
The control box used to be a separate thing made by Bitron, although I'm not
sure whether Pug use these any more, or whether the main engine ECU controls
the fans.
I'd like to be able to get enough information to test the special sensor.

Cheers,

- Steve