As STU says temp gauge sender, CTS on these is at back of head other side, right at the back by a water pipe, screws into a metal/alloy small plate that is held onto engine by two 6mm threaded bolts normally cap head allen screws, the water pipe there is also part of this.
Make sure that it is a proper cossie one you get as they are calibrated, which is what the coloured band is on them.
tabetha