Moin! Here I have a cheap power amplifier (~30 Euro, 4×150 Watt) which I have now connected directly to the battery after hours of attempts. There is nothing connected except the 4 loudspeakers (which are the standard in the E46). Even if no source is connected, it sounds like the part runs out once every 1.5 seconds. If you close what is on (e.g. iPod) the music is then stopped every 1.5 seconds short. Ignition is off, no other devices run… I don’t know any more advice…