I concur with Jeff. You should have continuity between the sender post and ground with the engine off. Either the connection is really, really dirty or the sender is shot. Just went through this on the 560, turned out the sender was bad.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.