head unit problems

I only have a sony head unit in my mk2 golf but it cuts out when it gets abit of bass not even that lound it cuts out and even worse when the engine not running so it seem like it not getting enough power which i know its not the car battery as it only a year old.
Someone rewired it but i havnt tounch it since i'v had the car if any one could give me some tips thanks

pete

 

Seems to be going into a protection mode. Re-check the wiring and I assume the speakers are adequate to handle the headunit.

 

Thanks will have a look and let you know just got to get a wiring diagram so i know whats what.

 

sounds like the speakers are wired the wrong way,they have a positive and negative side
what colours are on the head unit,ill see if i can match them to the car