On our recent group trip to Wales my travelling spare HD rectifier was fitted to another M3W for the 3rd time when it's CE rectifier started showing 16.6v on the move. I have never had to use it myself yet as the original CE item has not been a problem since the new chassis mount was used following a chassis change in 2015. When fitted to the original engine mount it consumed two of them. When we fitted the HD rectifier and confidently fired the car up it failed to produce anything! The bonus of travelling in a group is that another HD clone rectifier was produced and this fixed the problem, a steady 14.4v was restored.
My well travelled HD spare was binned, I maybe should have kept it for investigation but room was tight. Although I have had no problems with the CE rectifier since 2015 (20,000 miles) I will be getting another spare HD rectifier, hopefully just to help other M3W owners out. If you are still wondering what is the most useful display to show on the Speedo, it's definitely Voltage, time and miles don't matter if you have no volts.
