I possess a 2008 W639 model. A week ago, I encountered a starting issue characterised by a clicking sound. I successfully jump-started the vehicle, suspecting a depleted or low battery. The vehicle was operational and utilised as a delivery van throughout the day. After a few hours, the cluster ceased functioning, and the battery ultimately failed. A technician arrived, inspected the battery after a jump start, and confirmed everything was satisfactory; however, he said, "The engine-to-body ground connection is inadequate." Successfully established a connection from the engine block to the earth point beneath the bonnet as a temporary solution, and all functioned properly.
Yesterday, I installed a new earth strap from the gearbox to the body, intending to remedy the issue; but, it did not work. Commenced examination for other concerns and discovered that the original earth strap from the engine to the body was in satisfactory condition. The sole method to initiate the van's engine is by utilising a jump booster cable connecting the engine's positive terminal to the body’s earth point. I have inspected the battery negative, and it is functioning properly; also, all ground connections in the fuse box appear to be in good condition.