8 cylinder front engine iconic vehicle
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By h2pmr
while i have the dash apart i thought i would also check the calibration of the voltmeter.
an ideal "while you are in there already" job.
voltmeter on dash


on the rear of the voltmeter 12v feed is the red wire and the earth is the brown wire


metal disc on the side of the voltmeter is the adjustment potentiometer need a tiny screwdriver in the center slot to move it


if you don't have a power probe or voltage generator, here is an easy way.
assume the battery in the pictures below is on your daily driver car, not the 928 you are working on.

connect the brown wire from the back of the voltmeter to the battery earth and also the earth lead from a digital multi meter.


then connect the red wire from the voltmeter to the battery 12v terminal along with the 12v lead from the digital multi meter


and depending on how good your battery is you will get a reading as below


so the voltmeter SHOULD also now read the same as the digital multi meter, if not turn the little potentiometer, does not need turning very much to alter it
then start your car and again the voltmeter should read the same as the digital multi meter, approx 14v

hope this helps somebody :byewave:
worf, SeanR, Bertrand Daoust and 2 others liked this
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By Mrmerlin
NOTE before you re calibrate the gauge you should replace the fuse for the instrument cluster,
use D100 on everything electrical,
including the grounding points and the power supply wire connections .
NOTE$# you could see a big difference in the supply power that gets to the gauge after you do the cleaning,
thus negating the gauge re calibration
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