Bought a 1999 W220 S500L. Electrical gremlin! Help!

[Guinevere]

Gday Al,
So, as per the post heading.
The chap I bought from said it was overheating... a potential buyer who apparently has worked on 'hundreds of them' convinced him that it was #3 cylinder? on the left bank and the heads would have to come off etc.
I found no signs of head gasket issues, no yoghurt on oil cap or coolant reservoir, oil tasted & smelt good lol, no white smoke from exhaust etc engine runs smooth as also!
So I took a punt. Now in the driveway.
I watched the electrical temp reading from the climate control screen over a 20 km drive, highest temp shown was 92°C. Checked coolant level next day, no movement. Sweet.
The chap had seen a bunch of errors on the dash, and yes, one is saying overheating or similar.
I bought it with the cluster not showing anything, no lights, nothing. Dead as, with RPM stuck on 3500, Speedo about 50km/h etc.
However, today, after a lot of moisture and rain, it's working again, sort of!
It's flickering lights and needles are erratic etc.
The interior seat and button lights were not working, but now come on with the cluster.
Cluster fluros stay on though after full shutdown.
Now I know why he was keen to leave it sitting with the negative lead off the battery, to stop it going flat!
Fuse diagrams on the net are next to useless as they don't correlate mostly?
Anyway, cudos to Steve at a Perth dealer for pointing out the 3 cluster fuses. The lights went off after pulling the second fuse. #21 I think.

[Guinevere]

continued. (didn't want to lose a post due to time out... again argghhh!)

So, me thinks I have a bad connection somewhere.
I have run a continuity test over the back of every fuse, all ok, so none blown.
No apparent evidence of corrosion and fuse boxes and wiring look nice and clean.
I did check and push the fuses under the rear seat, but apart from that and the rain and moisture, nothing has changed.
Battery is fully charged, with cleaned clamps.
Any pointers where to start looking?
I joined this forum years ago, but never ended up buying my 'Guinevere', but I love my 'new' girl as she has no rust!
I am not even sure of the odometer kilometres yet, somewhere around 250k ?!
Reed valve is clean also, but I suspect it hasn't always been.
Does anyone know if the generic part (OBD II) of VCDS (VW) scan software works on MB ?
Hope we can solve this together.
Free beer for the winning solution!
Cheers
G

[stefcep]

Don't these cars have a know water damage issue?

https://www.youtube.com/watch?v=PRxx2a3NDYI

https://mbworld.org/forums/s-class-w220 ... e-box.html

Here is an encyclopedia on the W220

https://www.benzworld.org/forums/w220-s ... -here.html