Installed my new F90BT that i purchased of ebay. took me a little while to get all the necessary cables and everything all wired + soldered. after booting up the deck and fixing a couple of minor issues(ie. ebrake cable and backup cam.) Everything works fine, the only problem is that the audio only come out the front right speaker. if i fade to the back or left, nothing comes out.
I pulled the deck out last night, re-soldered the connections for the left and rear channels(both negative and positive) and still no audio out those channels.
It is like this no matter what output i am using. cd, radio, ipod cable..... 
My question is are my left and reach channels fried?
And if so, could i just buy a 4 channel amp and power my speakers using that in order to get around the problem?