Dear Mcollie
I had the same problem on my '95 C280. It turned out to be a silver box that simply plugs in to a socket. You will find it on the passenger side of the engine near the firewall. There was a short in the OVP circuit which is also located in the silver box. Some times it would complete a circuit and sometimes it would not. Mostly it would not. It took two seconds to pull the old one out and plug the new one in. I have had no problems since then.
I hope this helps someone out there. I spent $1,000.00 in mech. charges replacing everything from the fuel pump to sensors and my car was down for over 1 month.
Chalk it all up to an experience. Intermittent problems are the hardest of all and it drove both my mech. I nuts.
Best Regards and hope it helps.