My 996 has just started doing exactly the same thing on Sunday, at first I thought it was water loss, but the gauge moves too fast so like you say it must be electrical. First noticed it after passing through York centre in heavy traffic so thought the alternator was not coping at low revs, but a fast run to Helmsley then home did'nt change things. Going to check alternator output this week, but also wondered if this was some sort of voltage stabiliser for the gauge somewhere at the back of the instrument panel?
