SLK R170 Dashboard side indicators not working
 

I have recently bought an SLK r170 ( 2001), and there is no sign from dashboard side indicators left & right BATTERY, HANDBRAKE, CHECK ENGINE etc. it is always turned off, black, the main gauges FUEL, TEMP, SPEED etc. are working fine .
Is there any advice on which direction I should start the investigation first?
Thanks

I’ve removed the instrument cluster to find out that the previous owner had black-taped from the inside the symbol panels so no indicator was visible. I can’t imagine for what reason he did that but anyways the problem is solved.