W211 Interior Lights ETC Not Working

[Tompion]

Hi, I am hoping someone will have some knowledge relating to electrical issues on my 1987 Mercedes W211 E320CDi Sport.

None of the internal lights will work automatically or when buttons pressed on the overhead control panel. All bulbs, door switches, and fuses have been checked.
Command display does not change according to light levels (set to auto)
Intermittent wipers do not react to rain but just operate on a 5 second cycle.
Auto headlamps on all the time.
Alarm movement sensors also not working.
Phone cradle powers up in summer and otherwise after one hour of driving!

On checking the voltage to the rains sensor it was fluctuating at around 3-4 volts so I have removed the overhead panel and the voltage to it was doing the same. I identified a poor earth feed, so I have tightened the passenger footwell earthing point and that seemed to provide over 12.55 volts to the feed, so I put it all back together but no change whatsoever.

I have spent hours online researching similar issues but no one seems to post a fix, so I was wondering if this all points to the rear SAM playing up?
Anyone any nuggets of wisdom, please?
Thanks
John

 

[Tompion]

Fixed

I decided to check the voltage to the overhead panel again which was only about 3.5v. Therefore, I decided to go ahead and add a new earth (negative) to the plug. This has worked like a dream and everything appears to be sorted. I will go and check after dark and update this thread if needed.