Duration plus – where is it in the Audi 80 ?

When the car radio was installed, the source of all evils was finally discovered: my car radio is ONLY running on Schaltplus! The cable connection on which duration plus should be is dead (cut off, no voltage on it). In order to pull a new cable directly from the battery the time is missing at the moment, i.e. the question to all Audi 80 connoisseurs: Where do I get to the fast (and without risk to torch the car immediately) Lastplus? I would have guessed myself on ignition lock, but if possible would have had the color of the cable (93 Avant Quattro). Would be grateful for quick help, the mill is currently standing at Hifi people and no one knows further. Marc