gas gage

This is a known problem, this company even rebuilds the Instrument Cluster to solve this: http://www.bba-reman.com/content.aspx?content=Mercedes_300E For other common problems, look here: http://repairpal.com/mercedes-benz-300e-1990/common_problems

my gas guage registers 1/2 full all the time when I know its not

Mine was a fuse which is in the fuse box under the hood