Just digging into this thread. The added ground wire from the VDO has to go directly to the battery or engine ground. Going through the fuse panel is not helping at all. See link below and dowload FourWinns Dash module.
http://cdielectronics.com/Downloads/tab ... fault.aspxTrim Sender:
Secondly. Under your dash, pull the plug and check the resistance between the purple/white wire and ground. When the drive is down, the resistance should read 10-12 ohms.
If you are reading "open", then you may have sender issue.
If you are reading a resistance between 50 and 600 ohms, the sender is out of adjustment and out of the range of the VDO gauge. If it is out of adjustment, we can talk about that since it may require more than loosening the screws.