M104/1995 E320 ECU pin configuration identification
 

Does anyone know on either the ECU itself (behind the battery) or on the wiring harness socket where pins 10 or 21 or 9 would be? Do the numbers run vertically? Horizontally. I just spent ten-minutes scrutinizing the socket and the ECY pins with a magnifying glass and LED flashlight looking for numbers of any kind. It's really hard to check continuity between the coil power wire and the ECU when you can't identify pin #10...

The ECU Pins on a 1996 C280, M104
 

Having just replaced the coil pack wires on an M104, I have the diagram right on my desk. I printed it from Alldata, which indicates that it applies to Models 124, 202 and 210. It must be the same as yours - I replaced the wires going to pins 9,10 and 21. Mine has a 44 pin connector.

First of all, I would advise against bending, twisting, turning or even unnecesarilly touching anything associated with the wiring harness. Don't even stare at it too hard. You may want to put a mirror under the connector to help you with your testing.

If you could imagine holding that connector and looking at its pins, with the cable going out the left side, the pin in the lower right corner is number 1, and the lower left is 11. Then 12 is right above 1. 44 is in the upper left corner. So 10 and 9 are on the bottom row, one column over from the cable end, and 21 is right above 10.

Here is a pict of that connector

Thanks to you both, that info. is worth gold.