My father-in-law has designed and built robotic equipment and electrical components for 33+ years. He told me to never use emery cloth to clean electrical contacts. Instead, he said to use a pencil eraser. He said that all electrical contacts are coated to prevent corrosion and that emery cloth will remove the coating. The pencil eraser will clean any surface dirt without harming the coating. He told me that he has fixed million-dollar machinery with a simple pencil eraser. Who knew!?!?
I thought this might prove usefull to everyone here.