No idea what's happening. You do realise you're only supposed to connect the extra ground cable to the ECU mounting, don't you? e.g. bolts 1 or 3 in Davren's diagram. Not to the ECU itself.
i changed my battery recently and the faults i have lived with for the last year all dissappearedStart with a new battery, the biggest one that fits in the battery box (i have a 74Ah in my 1.6 Stilo).
There's a good chance all faults will disappear.....
Main thing is concentrate on a good chassis to battery negative earth. If that's OK then it's a safe assumption the rest of the chassis is at the same potential so no need to start checking the suspensionUpdate:
Removed the cluster, to check the connection. No corrosion or whatsoever, so I guess everything is OK with the cluster.
I'm thinking of adding a few extra earths because, even when adding those earths described in the guide, I still measure about 0.2-0.5V at so;me places :/ (For example at the front springs). But if this ain't working, I'm lost..