As a temp fix, remove the plug from the switch, fit a split pin between the two contacts on the plug, tape into place, fan will run all the time the ignition is on and car will run cooler, but better that then run the risk of blowing you head gasket.
|Get a new rad fan switch ASAP, remove split pin and re-connect plug, check coolent level.
My temp gauge reads very irraticaly. Sat in traffic or driving around slowly it shoots up to 100. but then sometimes it just settles down to normal. I dont know if it is connected but the petrol gauge does something similar.
It's suicide to switch it manually, unless you like doing head gaskets, stupid idea imo.
Look at the switch connector, how may wires does it have going to it, if it has two as I suspect then it is single speed fan, ie the switch simply acts as a on/off switch, bridge contacts see if fan runs, if it does buy new single speed switch, multi(2) speeds tend to be used on air con equipped cars, as uses slower speed for air con.