chytaan, if your S600 is anything like my 300SD, ahead of and above the battery is a distribution center. The positive cable splits into a couple of small cables and a big cable. One small cable goes to the fuse box above the battery. The other small cable and the big cable go the passenger footwell where there is another distribution center. From the front distribution center a small cable goes to the alternator, another to the starter, then there's a series of smaller wires I haven't investigated. I assume something goes to the ECU cluster and the front fuse box.

What's the point of this? Pulling fuses in a W140 might not localize a ground fault because the systems are interconnected. How the fuses even function as fuses is a mystery to me. Maybe your mechanic can isolate the circuit by disconnecting cables at these distribution centers.

In my case I'm chasing a draw that discharges my battery overnight. I localized it to the small cable that goes to the rear fusebox. I get the draw if any of a particular set of 5 or 6 fuses is in place. I haven't figured out what that set of fuses have in common (stereo, convenience module, and something else).

Sixto
93 300SD