After I replaced the tailgate wiring harnesses a couple of weeks ago, I realized I had no brake lights on the '92 245. I did the simple checks, and researched the problem here, which prompted me to recall that my departed '91 had the same problem a few years ago and the bulb-out sensor was the offending item. Not a great selection of junkyard Bricks out here in the desert and I was pressed for time, so I ordered one from fcpgroton and a few days later I was back in business.

So now I have two failed bulb-out sensors on my workbench. I've looked them over closely with a 5x loupe and I can't find any cold solder joints, burnt areas or any other obvious sign of damage. Does anyone have an idea of what the common failure mode of these is?
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In God We Trust. Everyone else, keep your hands where I can see them.