any chance your rca's came disconected if 1 came off your only feeding half the power

 

I said something because you can't tell AC poles apart using a DMM when both lines are hot... (if only one line was hot and the other was reference ground it would be a different story)

My thinking with the possibility of a bad ground is that the deck is putting out power into a 4ohm load now instead of stock speakers which maybe 8 or 10 ohms and may be suffering from voltage drop which was not an issue before....


just throwing that out there; but you should really go over all the wiring and connections.... 3x if need be....

 

Thanks for the input everyone. Some loose connections was the problem...must have came loose when the rear speakers were installed.