When the car gets to running temperature and i am stuck in traffic the fan turns on but the temperature gauge stays in the same position(in center).Does the focus have 2 speeds for the fan and the slow speed keeps the gauge in th center.2001 1.8tddi and it has a/c.

the ac fan has 2 speeds since its not warm right now and diesels run cooka it sounds like either the coolants low or the fan temperature switch is faulty or the thermostats stuck.

where abouts is the temperature switch please?

The temp gauge on the mk1 is very vague, so I would be very surprised if it did move tbh.
Is the diesel the same as the petrols, where there is no coolant sensors? The ecu measure cylinder head temp

would it come on if the coolant was low?the coolant was on min so topped up and its not come on since.

yeah if the coolants low it will come on coolant should sit between min and max

I cant see how it would come on with low coolant unless it caused it to overheat? how is it going to detect low coolant