Had the same problem on an 88 300SEL. Nobody pays any attention to them anyway. I drove down the street with lights flashing and horn honking right past a cop car. He didn't give it a thought. The control unit is generally in the passenger foot well. Remove the carpet and big protective board. The unit says Becker on it and has two plugs. CAUTION There is a plug connection in that area that is RED. Do not mess with the RED plug unless you want to deploy your air bag just to see if it works.
Good luck