Mike,

Thanks for letting me know that. I think I am on the right track. I found a used MAS on ebay for $49.00 plus shipping with the same part number as the one on my car (0115457932). The seller said there are a variety of MAS part numbers that will work the same.

Would you know what MAS stands for? It looks like they combined a couple of relays into one unit. I wonder if the knob on top allows it to be used for 1 or 2 fuel pump applications?

Also how do you replace the MAS?
It looks like there is a bracket attached to the firewall that needs to come off in order to disconnect or replace the MAS control unit.

The 1991 300SE is relatively new to me. I am just learning about it. I bought it on ebay and drove it home from PA to MA. It loves the passing lane and 80mph on the turnpike. Need to use cruise control to avoid getting a ticket.

Thanks,
Jack C.