Originally Posted by Red90
IME... The power side does not matter. They are designed to work with variable input voltage. The ground side can be an issue because if there is a voltage difference between the gauge ground and the sender ground, it will show up as a change in the reading.
I know this is a 2013 thread, but
Have experience watching the VDO gauge readings change from (+) current draw.
Here was the scenario:
Green circuit connection gauge reads fine.
Turn on the wiper motor, blower motor, and Lucas electrical defroster held to the flat windscreen with suction cups and the gauge reading falls.
Turn the wiper motor, electrical defroster, and blower motor off and the gauge reading goes back up.
Have no idea what the current draw was.
This was on our MGTD with a 45 Amp alternator upgrade compared to the 20 Amp generator.
Converted the original smiths tach to electrical impulses off the alternator upgrade.
It was cold and at night so the lights and driving lights were on as well.