what is this?

[Evelbist]

wire with a circular lug at both ends. currently screwed onto the "grille mount??" (did i describe that correctly?)

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[el dub]

ground jumper?

[Ghoste]

Yes.

[Evelbist]

does it attach to the core support?

[twodko]

Yes

[Mytur Binsdirti]

I have one of those on my early '69. I figured that it was owner added, but apparently it isn't.

[bill440rt]

My '69 has the cable as well. 
At first look it appears to be some kind of return cable to assist the linkage. However, it really doesn't seem to be doing much of anything. 

[tan top]

 got one too     ,    from what I can make out  , holds some tension on the leaver ,  

[John_Kunkel]

I'd say it's intended to limit the travel. 

[Just 6T9 CHGR]

My late '69 doesnt have that....

Pictured in the parts book but there is no listing for it (15-11-78)  Highest part is 15-11-74 which is a grommet for the handle rod 

[Ghoste]

Mine doesn't have it.  Early December build but a lot of owners since new.