Gauges move when turning lights on / off
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Joined: May 2001
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From: Finland
Gauges move when turning lights on / off
Apologize if this has been covered elsewhere, but I could not find it.
Today I took my '85 911 to hibernation and again when turning lights on
or off the gauges move, some up, some down. Fuel goes down and oil
temp goes up. Also oil pressure is reading a steady 1Bar when ignition
on but engine not running. Reading 4 - 5 Bar when engine running and
is moving with RPM.
There is probably some where a voltage regulator that should keep the
voltage to the gauges constant, but where?
Also my gas gauge is not very accurate, changed the sensor in tank with
an new, Porsche part, but that didn't help.
Today I took my '85 911 to hibernation and again when turning lights on
or off the gauges move, some up, some down. Fuel goes down and oil
temp goes up. Also oil pressure is reading a steady 1Bar when ignition
on but engine not running. Reading 4 - 5 Bar when engine running and
is moving with RPM.
There is probably some where a voltage regulator that should keep the
voltage to the gauges constant, but where?
Also my gas gauge is not very accurate, changed the sensor in tank with
an new, Porsche part, but that didn't help.
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Most likely a bad/weak ground connection in the gauge area. When you turn on the lights, the backlighting on the gauges draws current and creates a voltage offset across the bad/weak ground connection point.
This ground point is the reference for the gauges, too. The voltage offset moves the reference causing the gauge needles move too.
This ground point is the reference for the gauges, too. The voltage offset moves the reference causing the gauge needles move too.
Race Car
Joined: May 2003
Posts: 4,240
Likes: 103
From: SoCal
Most likely a bad/weak ground connection in the gauge area. When you turn on the lights, the backlighting on the gauges draws current and creates a voltage offset across the bad/weak ground connection point.
This ground point is the reference for the gauges, too. The voltage offset moves the reference causing the gauge needles move too.
This ground point is the reference for the gauges, too. The voltage offset moves the reference causing the gauge needles move too.
e.g. 12.5 volts with the lights off and 12.0 volts with the lights on to the gauges.
Measure the voltage at the gauge of concern to determine the actual problem,
i.e. both the power and ground side independently.
