?Apparently the stock alternator of the SLK cannot provide enough output current to sustain the small 500w amplifier I installed in the back trunk area. If I turn up the volume the interior dash lighting and front headlights fluctuate in brightness when a heavy bass beat is produced. 

I may have to update the alternator to a higher amperage model, I’ve had this issue with other high power stereo systems in the past. Nothing new.