Not sure on the early ones if the fan was ECU controlled or not, if so could be EMS has detected a fault and put fans on.

More likely though they are switch controlled due to age, so first find the fan switch, this will be in the radiator or the thermostat housing, unplug the electrical connector, if fans still stay on it shows the relay is jammed normally a "tap" on it will unjam.

If the fans continue however this points to a faulty fan switch which is unlikely though.

I certainly would not rewire to a switch though this means you would have to switch on/off manually when they were needed and if you don't then your in trouble, hence why it is a automated system to start with, not to mention you are only "Working around" the problem rather than fixing it.

Martin