whats it worth

[Mr70]

It was a new extra cost separate option,that also came included in the OCG for the 1970 Impala-Biscayne-Belair-Caprice & their Station Wagons.
Other GM brands had it possible under a different name too,as Helmut shows.
As has been said,it delayed the headlights & interior lights from turning off right away after you turned the car off,and gave you more time with em on.
Like having to open a garage door or staying in the car a lil longer.
I pulled one out of a '70 Caprice and sold it for $50 about 15 years ago,that was about as complete as yours.
The guy that bought it,installed it in his '70 Impala & I believe belonged to this site,but I can't recall his ID name.
I saw one in a 1970 Malibu once @ the 1988 NCOA Peoria Chevelle Showdown that had it,but I never found out if it was factory installed,dealer installed or owner installed.
I have a filmstrip & booklet somewhere that goes into more detail about it,but here's a small overview.