The EA wiring is separate from the engine harness. It is my understanding that all early M104s had wiriing issues in both the engine harness and the EA. I have rewired 3 EA's to date for E320 and 300E models. If you can get to the cable that runs into your EA and cut a 2-3" slice in the outer sheathing, you can tell if the insulation on the wires inside is flaking.

I wrote a rewiring tutorial for the M104's and posted it on benzworld. I did'n post it here because I couldn't make the .pdf small enough with the illustrations to meet the upload criteria for this site.