Back to Rob's initial inquiry... I have a little to add on the subject, even if I'm late to the party.
This is what my coworker has wired up to control the lockup in his TH350C. It's in a 60 something Impala. It's not perfect, but I think it looks pretty clean. I can ask about the specific switch he used if
@SirRobyn0 is interested.
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My old man uses a lighted rocker switch on the dash to control 3rd gear lock up in his 200-4R. I got no pics of that install, but it's something like shown below. It's convenient because it lights up when the converter is locked. No second guessing it for any reason.
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