When signal lights are on just loud buzzing sound on 1981 380sl Mercedes what is problem?

It could be a number of things...eletrical problems can be a nightmare. It sounds like you have a problem with your hazard light switch...the big square red button on the shift console. Has this car, and in particular, the hazard switch been exposed to water, extreme dampness...any moisture at all. Do you live near the beach? Did you spill any liquid in the button's area? All of your signal lights are tied into that unit. Also, the problem might be in the turn signal switch on the steering colum. Does the turn signal lever feel very loose? Does it feel like it clicks into place when you move the lever to signal left or right? Does it feel warn out? Does it function properly? And, if those aren't the problems...most likely its a bad relay, which is usually found on the right side foot well, above the fuse panel access. There are about a dozen or so relays there....and unless you're familiar with the color codes or schematics, don't even start to mess with it...it will drive you insane. Most MB mechanics don't have a clue either. I hope this helps you. DM