My 1.9dci 2002 scenic has developed a temp gauge fault when driving the temp gauge can climb right up past the red but car engine temp is actually normal. if I Turn the lights on from side lights up to fullbeam the temp gauge gets higher and higher the more I turn things on like radio or heater and as soon as I turn them down or off the temp gauge will drop with each item I turn off. It can be likethis for weeks on end then I can have weeks when it works perfectly normal I am guessing it's a bad earth as change the temp sensor which did nothing also a few weeks before this started I had the alternator bearing changed and auxillery belt. I have tested the current on battery and what the alternator is sending to the bbattery and all are normal. The temp gauge is the only one playing up if anyone can help with suggestions for where it could be earthed or possible other solutions I would be graeful as when I asked electric guy he said to re earth the whole car at vast exspense