Does the temp sensor just interrupt the live feed to the fan i.e.
Live feed to one of the sensor terminals
Other terminal to fan live
Fan earth to chassis

(Yes, you're right, I should have taken a pic of the old wiring)

[Edited on 7/2/10 by norfolkluego]

Thats how iv done mine

Thats right but I have always put a seperate manual switch in so when sat on the Start/finish line I can have the fan running.

I suppose it realy depends on the current that the fan is going to draw.

It may work for a while - why not have the sensor switching a relay and that handling the power for the fan.
If you do it this way, you can use any switch to overide the sensor and switch the fan on.

Len.

I would use a relay !