W201 190D Stereo??????!!!!!!!!!

[TomEL]

Anyone got the foggiest how the to get the original stereo to work in a 1988 Merc 190D 2.5? I've pressed everything, and with it on full volume I can still only just hear a hissing sound, like static. The display just shows two digital, horizontal dashes or occassionally says code on the dispaly. Any ideas?
Thanks Tom.