Solved:
It's an Empeg, so it couldn't be really dead. I breathed some air thru the plugs and disconnected and connected every connector inside so it would have a proper connection (without dust).

Well, it works! Yeah.

Why did I reanimate my Empeg? I am owner of the german Volkawagen Scirocco Forum (www.sciroccoforum.de). In 2006 the girls and boys of that forum gave me a Scirocco as a present. Yes, a real car, built in a whole year with parts and help of 100 people. And for this car nothing is good as a car stereo less than an Empeg.

Oh, I love my car (www.koenigsrocco.de) and the Empeg .

best regards from sunny Germany,
Rolf