This might be of some help but a few years ago my 2011Roadster would now and then lose all power to the Speedo and tacho, with help of this forum i found and fixed the problem. There is a single purple wire coming from the fuse box to the large main harness near the steering head. It branches into two wires which power the speedo and tacho, see my photo below. The join was corroded badly, I cut open the harness, clean the wires, repaired and no more problems.
