1983 mercedes 300 sd. you already replaced the glow control relay but it still makes a buzzing sound and you go to start the car. if you rotate the car key to start it nothing happens. what's the problm?

AnswerPerhaps when the glow control relay went bad, the contacts stuck closed causing the glow plugs to burn out. It happened to me, I had to replace all the glow plugs. It now starts every time.

The glow plug relay could be bad, poor contacts on the fuse or plug contacts to the relay. Obvious reason is a week battery.