Hello Hans,

Wellcome and good luck with your V8.
As you already indicate yourself, the batteries are not the problem, since turning the key in the driversdoor also does not seem to work.
How is your German? We have a good Search funktion, with obviously more leads in German than in English.
In German search for "Zentralverriegelung" or "ZV". I am sure there is a lot of material on this.
And yes, the control unit should be close to the battery.

regards,
Eric

P.S. Where in the Netherlands do you live? I am from there as well, and sometimes I come over for a visit.