I have a 1998 slk230 with high milage that is my teenage daughters car.
Today it wouldnt start for her when she got out of school. I put jumper cables on it and it would crank just fine, just not firing at all. Got it towed home and after a little research I discovered there was a blown fuse (#11 ignition coil voltage supply) in the fuse box on the right side by the firewall. I put a new fuse in and it cranked right up. I figured a shorted wire is what blew the fuse so I start moving wires from the coils packs (by the fuel rail) and the first wire I touched blew the fuse again, it stalled. Taking a closer look I notice the harness is routed up against a lift hook on top of the engine right before where the harness goes to the coil packs. I peeled the cloth tape back (real brittle when its 13 years old) and found a bare wire that was grounding out. improper tape job and a 20 cents fuse and we're good.
I am probably the only person this could happen to but thought I'd share anyway.

Picture #1 : Fuse box in engine compartment, drivers side (the states) by fire wall. #11 has the fuse out in this picture - right column second down.

Picture #2 : Wiring harness to the coil packs by the lift hook on top of engine. It was up tight against the lift hook, this picture is after I peeled the clothtape back.

Picture #3 : A different angle of harness by fuelrail routed against lifthook to coils.

Picture #4 : Bare wire -not good. I always wonder how something like this would work out at a dealership shop.