<p>Matthew:<br>
Although the contacts and switch mechanism appear to be free of corrosion, it sounds like it could be a simple contact problem with the wiring that governs the slow shutter speed warning light. Another unlikely culprit could be that the previous owner may have done a lot of low light and longtime exposure photography and that the bulb/indicator light is burned out. As long as the exposure is in progress, the yellow light will remain illuminated.</p>