hosrom_951

Grounds, there are two under the dash at the driver's side. And check/clean the negative battery cables. I replace those cables with Ice Shark's kit along with a suppliment ground wire and things are great now.

Charlotte944

Its not the gage. Its how the gage cluster and the entire electrical system are designed.

With the exception of the voltage regulator in the alternator and some "onboard" regulators in the DME, there is no external voltage regulation.

Turning something on and off (like the brake lights, turn signals or emergency flashers) causes brief changes in voltage throughout the electrical system.

Because the gages and sensors are referenced to ground potential (0 volts), a decrease in the applied voltage causes the gage to indicate "higher."

To get a more "stable" monitoring system would require regulated voltages below 12 volts for both sensors and gages. This is one reason Porsche went from using unregulated 8 volts to regulated 5 volts for the AFM reference in the '85.5 and later models.

In the early cars an unregulated 8 volt reference to the AFM is supplied by the DME via a resistive voltage divider. Because this reference is not regulated, changes in system voltage cause chages to the AFM reference.

By lowering the reference to 5 volts and using a voltage regulator, the reference to the AFM does not change with changes in system voltage.