Problem started with alarm arming itself and going off. Car was running great, and even running great with alarm going off on the way home!!!! Read how to disconnect alarm under the passenger floor by disconnecting two harnesses to Becker black box. Alarm stopped!! But now the car just cranks over with no starting. Reconnected harnesses and alarm starts all over again and no starting.
Two separate problems? I sprayed starting fluid, car started and ran long enough to burn off starting fluid. Ahah, no fuel action! Fuel pump relay fairly new. Jumped out pins in connector block for relay, car still did not start. Very low voltage on positive side of connector block. Jumped other side directly to battery, and presto! Car started instantly and ran fine. But cannot be driven this way of course. Where does the power come from to this relay? Ignition switch? Fuse? Can someone help before I have to pay Mercedes big dollar to diagnose? Oh yeah, it is a well maintained low mileage 1988 420sel. Thanks, Steve