I recently managed to get an (almost) complete Twilight Sentinel / Auto-Headlight setup (switch, amplifier and wiring) from a '76 Cadillac parts car which should be plug-and-play with my '75 98 Regency.

The only issue is I wasn't able to grab the photo-cell / light sensor as aparently someone just cut the wire and pulled it alongside the entire dash-pad that is was mounted in to and finding a replacement is turning out to be more difficult than I would have thought, so if anyone has one they could send my way I would greatly appreciate it.

I'm also looking for the left-side dash plate that has the Twilight Sentinel and Pulse Wipers applique on it (I'll attatch a photo for reference) as well so I can swap it out and have the proper markings for the TS option, so if anyone has one of those they can part with that would also be fantastic.

 

I can tell you I have never seen this option on a Delta 88. I have stripped down 25 or so, the vast majority of these being 74-75 Delta 88's.
John Capone 98Regency would be the man I'd contact.