Seen this movie. In my case when I jumpered pins 1 & 2 in the MAS, the fuel pump ran and car started, indicating the fuel pump relay incorporated into the MAS was bad. A new MAS got me going again. I'm not trying to make a point about the MAS itself, just pointing out that it contains the fuel pump relay in some models.

I see yours is a 93 300E. Out of curiosity, I looked up your model at this site parts data base and saw that neither the 2.8l or 3.2l 93 300E have a MAS. I'm assuming this is not an over-sight. If it's not, that's good for you because you must then have an independent fuel pump relay which costs WAY less than a MAS unit.

I didn't read everything prior to this. Has your fuel pump relay been replaced?

I had simular problem with my 1993 300e. Towed to the machanic - off the tow truck started right up. Mechanic had it for two weeks - started all the time . Finally drove the car home . Next day no start. Than the help of MB forums I was cheking thing out under the hood. The top of the OVP relay I had a broken fuse. Changed the fuse, now the car starts all the time. PS. I ordered a new OVP relay