67 Impala SS - Horn- Is this factory installed??

[HPMIKE]

I recently picked up this survivor 67 Impala SS. It's a mint, one owner original 396 car with 25K original miles. While I was going over it I assumed that the "auxiliary" horn is an aftermarket piece. Now I am not so sure, as it has a correct color coded "jumper" harness that ties into the regular dual horns and the terminal ends are all original style. Also the way it mounts to the inner fender is really not typical of anything aftermarket. I am admittedly a Mopar specialist and am not fully tuned in on all of the variations, so any help would be appreciated.

Thanks

MB

See att for the pic of the horn.