I have seen multiple posts on this issue, but often without resolution. My 2006 Mini R53 had the issue where the tach would sometimes lose power and then come back on, other times the speedo and temp gauge would drop to zero and bounce up and down along with the brake and service-engine-soon warning lights flashing. Then it would all go away and everything would be normal for varying lengths of time. I traced wiring, checked grounds, replaced all 4 wheel-speed sensors and got nowhere.

Then I ran across a post where someone with the identical problem removed the tach and the problem went away. I tried that for a couple of days with the same result - no more crazy gauges. I bought a used tach on eBay, and so far, the problem is gone.

I know this is an old issue, but I have only had my 06 Cooper S for about 18 months and finding the fix took a while. Thought I would post the fix in case anyone else is still chasing this problem. Seems as if it is pretty common.