It hit me last night, my 94 E420 would not start. I could hear from the inside of the car a buzzing noise. Look under the hood and discover the buzzing noise coming from the combination module relay, located behind the fuses on drivers side firewall. I could not see any problem with any of the fuses due mainly because it was dark. The next morning I reinspected the fuses in daylight and there it was FUSE #5 with a hair line crack. So I replace the fuse, hit the ignition switch and then she fired up with no problem.