Cigarette Lighter Problem - Disk Protection on 1995 Toyota Camry

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I have a 1995 Camry XLE, whose cigarette lighter stopped working last night (I was using it to power a 117v Inverter). I checked the fuse, which was OK, then checked power to the cigarette lighter with a voltmeter, which was also OK. I then checked the continuity between the lighter power terminals, and the inside of the lighter, and found an "open" between the terminal for the center pin and the power terminal. When I disassembled the cigarette lighter, I found a metal disk (looks like a washer) which tested "open" which was installed between two parts of the power terminal for the lighter. When I reassembled the lighter without this disk, it works fine! Does anyone know what this disk is and what its purpose is (I assume it is providing some kind of protection)
(1) Answer
It's hard to say without seeing this, but it's there for a reason. These lighter sockets can generate a lot of heat, so it may be a heat sink that absorbs heat to prevent damage to another part in the assembly.