I have a question reguarding the engine in my 1985 300D Turbo not starting. When I try to start it, everything seems okay (the glow plugs appear to warm up, but I really don't know) but the engine doesn't crank at all. Also when I go to turn the key, there is a horrible whining noise coming from the engine. I opened up the hood and the noise is coming from a black rectangular box on the passenger side, behind the headlight.

So I was wondering if anyone knew what this box was, and all I need to do is replace it? If anybody can give me any advice on what could be the problem and how to fix it, it would be greatly appreciated.

Thank you in advance for helping about someone who doesn't know anything about engines.