Probably get flamed but here goes:

Try spanking and telling him NO! Consequences for actions, even at 3 years old. I'd much rather spank than have him electrocuted or something heavy fall on him and crush him. That is a cause for spanking because he's putting himself in danger.

Keep him out of the room when someone isn't there to supervise him. And when you're in the room with him, make it known to him he's not to touch it. He should be learning rules of behavior by now.

I was at the DMV today and there was a little boy that had everyone's attention simply because he was hitting, biting, kicking his mother the entire time she was conducting her business at the counter. She did absolutely nothing -- she'd look at him and smile and say 'cute' things to him. And he'd smack her in the face. He tried to destroy the counter but that didn't happen. Oh, he tried -- kicking it and when she was holding him trying to knock everything off the counter. Trying to pull off the vision test machine. She did nothing.