you were right VTS 123.... it was somewhere down.
I went to a Citroen Tuner in Amsterdam who found it and connected it.
They also did a diagnostic check..... NO errors.
I will have to come back thursday as they are going to check my electrical circuit according to a Citroen scheme.
The problem still occurs when they turned on the lights/radio/alarm lights/heater my saxo dropped dead and went out.
They checked the alternator and battery and cleaned another thing (in dutch STAPPENMOTOR and in english i have no idea stappen = steps motor= engine).
So the problem still occurs