I doubt the the wiring would be in place if the car wasn't ordered from the factory with the third brake light.

By 1997 year model, the third brake light was mainly only standard in the U.S. market. All other markets could have one fitted at extra cost.

Also, to achieve the "original" look, I guess you will have to order also a new rear parcel shelf.

A. Rosich
S320, 1998
E320T, 1995