UK Car Repair: 1997 Astra Temp gauge, voltage stabilizer, electrical connection

Question
Hi

Recently had a problem with the alternator on my 1997 Astra, 1.4L petrol. I replaced it after getting a tow truck to bring me home. However, now the temp gauge won't work properly. It sits at the blue line unless I'm driving below 60mph when it starts to rise a little and then falls as my speed drops.

Other than replacing the alternator, i also replaced the battery at the same time so I was thinking it might be some sort of an electrical connection problem.

Any ideas?

Thanks

Answer
It sounds as though the voltage stabilizer is not working, this is supposed to keep the supply voltage fairly constant, that way they will remain accurate.  In this case the gauge seems to be reacting directly to battery voltage which can be from below 12 to above 14. Check that all of the alternator connections are correct and secure.