LED lightsets that are used outdoors are prone to water leakage and subsequent corrosion of the LED leads inside the sockets. Pull the LED's out of their respective sockets in the string. If the leads are rusty, the LED's will need to be replaced. Don't try to clean them if they are rusty. The sockets can be cleaned with a bit of WD-40 and a small screwdriver (please do this with the string unplugged). New LED's can be inserted into the holders. Pay attention to the orientation of the LED's in the sockets. There is usually an indicator on the LED holder that shows a "long" side and a "short" side. Place the new LED into the socket with the long wire on the long side, short wire on the short side. Bend the leads back slowly. They are steel and are not as flexible as brass or bronze leads that are common on the older mini-bulbs. Stop by the automotive dept. and buy a tube of dielectric grease. Squirt some of that grease into each socket before you place a new LED into the socket. That will prevent further corrosion. When you buy new LED strings pull each LED out and coat the contacts in each socket with the dielectric grease before you place the string into service. Replace the LED's back into the sockets, push the securing tab down and your new corrosion proofed lights should last a very long time time. Good luck!