head unit only powers up for 2 seconds?

 Hi all. please forgive me if I,ve posted in the wrong section of the forum,

A friend of mine bought a new stereo for his Audi A3. He took it somewhere to be fitted and the geezer at the garage said the new head unit powered up for a short period then switched itself off. His conclusion was that the head unit was knackered so it got sent back to the supplier. The unit was tested at the factory and worked perfectly.

(I,m not sure if the bloke at the garage altered any of the wiring, would the head unit do this if it wasn,t earthed I wonder?)

Andy

PS

Well done guys, I entered the same problem on 2 forums & you were the first to reply. I know where I,ll come back to in future.  

All modern day radios need 2 power sources.  The yellow wire of the deck should receive constant power.  The red wire of the deck needs to be supplied with 12 volts only when the key is on. 

The car only has one wire that supplies power & that power is constant, there is no wire from a swiched power source. (I also thought that was strange)

Would it be ok to wire both the red & yellow wires to the constant power source?