The car suddenly turned off....Advice neede, please..!!!

Yesterday evening, the car suddenly turned off by herself while at idle…
Had been using the car for the whole day, and nothing went wrong. But while talking to a friend and leaving the car idleing, she became dead.
At first, I thought about the battery…put a new one and nothing happened.
The digital clock in the cluster is working, but when I turn the ignition key on, turns off. Even the alternator red indicator is off. This morning, tried to start the car again, and the alternator indicator dimmed for a second, and off again. The car seems dead.
Any idea, please?
The car: april, 1982, GTI 1600.

TIA and best regards….

Possible ignition switch wiring ?

Pull the red/black wire off the starter motor and touch a wire from the + on the battery to the terminal on the starter motor. If it turns over and fires up it may be your ignition switch?