I have a Haynes manual published in England for the entire 124 series. It is heavily weighted toward the '92-'95 models, has just bits and pieces of the information needed and wiring diagrams that will get you into real trouble. Its illustrations are crude and best of all, it is easily available for about $30 from Performance Products in CA. (800)243-1220. I keep looking for the M-B CD for some reliable information on my '89 300E but they always seem to be "out of stock"
I know nothing of the Popular Mechanics or ALLDATA products, but I would love to know if they provide better information than I'm getting now.