threeblades

Hi, I have a strange problem and have been a bit around the houses to try to identify it. Car is Fabia 1.2 mk2 so not complex. When the ignition is turned on, all is well and the required lights go on and off. Car starts fine and the tacho reads fine for about 2 to 4 sec. Then the tacho drops to zero and many (but not all) of the instrument lights don't work. I fitted a new battery as the old one was less than perfect but no change. The battery voltage is 12.5 before starting and jumps to 14.4 at the same few seconds after starting. If i turn on the headlights and fan together the load causes the voltage at the battery to drop down to about 12.7 for a second max before going back to 14v. Again, during that second of lower voltage the tacho works again. Clearly there is something that is cutting in to protect the instruments at a voltage a bit lower than it should be. Does anybody have any idea if there is an instrument circuit protector somewhere as I dont think this is an issue with the main voltage regulator on the alternator ? Many thanks TB