What does this clutch switch do?

TrailBeast said

Like already mentioned, if it's activated by the brake pedal it is the brakelight switch (and is what it looks like).
If it's activated by the clutch pedal then it is being used as a clutch safety switch, and is what keeps the starter from turning the engine over unless the clutch is depressed.
That type of switch could work for either one depending on which pedal activates it.

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Thanks everyone for chiming in. Did this only come on certain year 4 speed pedal setups? Maybe the rebuilt manual pedal assembly I bought was from a later a body like 71 or 72. Would my 67 dart 4 speed originally have this part on it? I'm wondering if my dart never had a provision for this? I could just run without it or just never plug it in? Are these easy to find. I need a replacement.