70' Dart Swinger Rallye Dash mystery hole ??
Its a cigarette lighter. The '70 cars could have as many as 3. There was a thread on here awhile back, maybe I can find it.
***Update***
Here it is. Thread explaining the extra dash lighter
http://www.forabodiesonly.com/mopar/showthread.php?t=39044&highlight=rally+dash+hole
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