When the contacts of a device are rusted or oxidized, the circuit that it normally establishes may be sporadic at best and completely disrupted at worst. On occasion, the damage may be so extensive that the device cannot be salvaged because the oxidation has penetrated plating or other surfaces to corrode much more deeply. Otherwise, you can use various brushes or cleaners, or both, to clean and restore oxidized contacts.
Cleaners for oxidized contacts include Caig DeoxIT—recommended by Boeing, Bose Corp., Xerox and others—and a range of contact cleaners for electro contacts and precision contacts from LPS Laboratories. LPS contact cleaners include nonflammable versions safe on plastics, nonflammable versions safe on most surfaces, and a flammable version safe on plastics only. The LPS website provides full specifications and recommended applications for each cleaner. If you have them on hand or can find them more easily at a nearby shop, some more general-purpose cleaners like Simple Green or NEVR-DULL Wadding Polish might do the trick. Any remaining haze or residue can usually be removed with a pencil eraser and/or a soft cloth.
A wire brush or fiberglass pencil brush will often abrade most or all contaminants of a surface. When retracted into the shaft of the brush, the hairs become stiffer, which allows for more vigorous cleaning of oxidized contacts. Don't scrub with abandon, however. Apply a fiberglass pencil brush with care, since you want to abrade only the oxidized film, not also the metal or plastic underneath. The Excelta Corp., which sells a variety of brushes, reports that its Fiberglass Scratch Brush is intended for "fine deburring, polishing, rust removal, or cleaning and erasing in chemical etching processes." Contact cleaning is also a listed use. Other vendors of fiberglass scratch brushes include Widget Supply, Pemro, Micro-Tools, Cumberland Electronics and sellers of jewelry-making supplies like Contenti.
Cleaning the oxidized contracts and other junctures of complex equipment may require special procedures, especially if tricky disassembly and reassembly are required. At Dana Sawyer's website on restoring a Schober Recital organ, the publisher recommends the familiar DeoxIT to clean the gold spring contacts of the organ and provides detailed instructions for reaching the various parts that need to be cleaned, as well as explanations of what to expect when contacts are treated and how to test whether your cleaning is successful.