Infra red locking system

I own a 1995 500S 4-door. Recently the door locks became unresponsive when I attempted to lock the car with the hand held infra red activator. The plungers in the doors functioned, but the locks did not operate. Also, the handle on the trunk that extends when you push the open button on the trunk door does not extend when the trunk is opened.

I have had trouble with the engine warning light remaining on all the time and no one seems to be able to detect and cure the problem. Any suggestions.

[semi]

replace central locking vacuum pump under rear passenger seat ($450).