Volvo Repair: Erratic Temperature Gauge, voltage stabilzer, temperature gauge

Question
75 Volvo 242 with an M41 transmission and I think a B30.

Recently my cousin in law replaced the clutch on my car and when it came back the temperature gauge was hay wire.  Im in Sacramento and the days are averaging 110 degrees.  Basicly the problem is this, when i rev the engine the temperature gauge shoots up all the way to the top and when i idle it drops all the way to the botom.  I need to know if its a faulty censor or what.  Thanks for the responce.

Answer
Chris, that car has a B20 in it.  Sounds to be to be a few things.  The Temp sender on the block.  The wire in the harness is probably chaffed bad.  You may want to run a new wire from the sensor to the junction block on the harness. The Voltage stabilzer on the back of the instrument cluster(looks like a small oil pan) and lastly the gauge itself can be going haywire after 31 years.  Hope this helped.  Roger