Button on shifter

I have just received a 1993 SHO with automatic transmission and there is no owners manual with the car. Can someone please tell me what the function / purpose of the little button the gear shift, left side. It is below the button you press to move the shifter out of park.

Also, is there by chance a place to download on line an owner manual.

In advance, thanks for the help

It is the button to turn over-drive (O/D) on or off. Press it and a light should come on in the dash that says "O/D off." As far as the owners manual you might be able to find one on eBay.

Or order a new manual from the dealer.
That should be the OD button.

Thanks for the replies. When I pressed the button I did not notice any light on the dash. The only light I see flashing sometimes is the one that says, Air Bag.