Unplugged, but why.....

[Soundmound]

Found this pigtail unplugged on my trucks transmission today and wondered why someone would have done it. '84 2wd 305 w/700R4

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[CheemsK1500]

I think that is the harness that comes off of the switch behind the brake pedal. I don't remember exactly what that switch does, but I think it controls your transmission lockup.

Edit, it looks like that's exactly what it is. Perhaps someone was having issues with it locking up at the wrong time, or the brake pedal switch was malfunctioning.