was about 3 years ago - all i remember was the cover was all black plastic, opened it, full of grease, cleaned it out (think i flushed it with wd40) put it back together and it worked. you can see how when the jack is inserted that it lifts the contact bar off one set of terminals and makes contact with another. its normal operation was only possible when the cover was replaced( again im trying to remember)

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pretty sure you can meter it out first to see if its working or not. if you open it up you have to force it by drilling out plastic rivets so check it first with a meter