I have a 1999 E-320 and I am having AM reception problems with my radio. When the engine is off I can receive AM reception okay, but when I start the engine all I hear is static. The FM reception is pretty good all the time. Unfortunately my favorite stations are on AM stations. The radio is original equipment.

Bring a small portable AM radio into the car and see if you still experiance the same problem.

If so, it is likely that an engine component is the source of interferance instead of an antenna problem.

Usually AM problems eminate from an absence of complete ground circuit from the antenna....If you pull the radio and check the resistance of the ground on the antenna plug (outside part of connector) to ground that will tell you everything...For good reception it needs to be 0.00 resistance to ground of the car body. If it is not than depending on how far away from ground it is will determine the lack of reception quality. Problems can be anything from bad ground at the car body to corroded ground shield in the antenna cable....Can also be an internal antenna problem.

__________________
83 300CDTurbo 307,000
2005 Honda Element 266,000
56 Nash Ambassador Country Club Special 34,000(under restoration presently)

http://www.peachparts.com/shopforum/car-audio-multimedia/125099-123-install-extreme-dynamat.html

Had that problem..the cure..

The antenna in the back window has a connector ...as you look back ..just to the right of of rear window behind the panel between the window and the door, just about where the panel meets the head liner. You will see a small
screw on "coax" connector. mine was not screwed on tight. FM worked ok but AM
was bad. just stuck my finger up there and tightened the connector a bit and no more problems.

__________________
1999 E300 TurboDiesel
2007 Ford Explorer limited
1981 John Deere 650 Diesel tractor

where is the connector/antenna in a E320 wagon ???

I also have bad (weak) AM on a Becker in a 2000 E320 wagon. The reason, I believe, is that the rear side window-embedded antenana is shaped much like the old style "folded dipole", the most elementary antenna used for FM. It was useless for AM; in fact audio gear that had both AM and FM provided a coil type antenna separately on the back for AM. In some areas I cannot get even the strongest AM station that I used to be able receive clearly in my previous MB. The fault, I am told, is that MB wanted the uncluttered look without an outside antenna, but the window style doesn't work for AM. I would be happy to hear any ideas myself!