Why doesnt your check engine light work did diagnostics on it everything is fine changed bulb but it still doesnt come on 1989 Mercedes 190e 2.6?

like any electrical bulb, it could be the socket, a connector or the output (from the computer). If it's that important to you, you could test it out, see where each point along the wire has signal. On the other hand, if you have a code scanner, you can use that to find out the status of the vehicle diagnostics.