mate ive spent the last three days wiring my sound system in on my leafy and my previouse owner was an absoult butcher with auto electrics.
so when installing a sub, amp and deck, aswell as 6x9s and 6.5s i have finaly got it all done i used a sony wiring kit for the amp aswell. so im guessing u have already replaced the speeker wires.
dont worry about using any of the wiring harness strait to the deck. your trying to run a deck that puts out 200watts (in my case) of a wiring harness that would normaly run an AM or possibly a tape deck in ur case radio, as a result it wouldnt get enough power and cut out.
so to fix that problem i tapped into the ignition wire about 10cm from the ignition barrel (i had to replace all the wire around there aswell due to previouse owners but u shouldnt have to) the wire u want to tap is white with a black stripe. run ur tapped wire (i used 3mm) to a relay in behind ur deck as an activation positive. then run a nice fat wire to the batterie as a power wire for the relay. obviously run a decent earth wire from the relay.
then from the power output on the relay into the red wire on the deck. this replaces the accessories wire that u have pulled from the cigeret lighter and that now activates the relay.
finaly that was all good and the deck wouldnt cutout anymore at high volumes or when brakes hit etc (the brake lights and clock and cigeret and deck all run of that same white with a black stripe thats alot of stress on a 2mm wire)
my next problem was your problem. this time i tapped into the "hot" wire on the relay and ran it strait to the yellow wire on your deck. then use the good solid earth u made on the relay as an earth for the deck aswell by running your deck earth into it. after doing this you will have full 12volts to your deck as an ignition wire (it runs of this) full 12 volts as a power wire (runs its memory of this)
lol now i have the problem that my alternator dosent put out enough power to run my amp at full power

its never ending
in my case i had a kenwood deck. and yellow is constant power. and red is powered when the igntion comes on.
i know it sounds like alot but i spent 2 good day i recon atleast 6 hours it took me maybee 2 hours to re run all the wires once i bit the bullet and did it all again i would realy suggest u do it. how i mentiond above.
idk what ur previous wiring was like but heres what mine looked like. those wires run to the ignition barrel and were TWISTED

together.
here is the clip that is ment to join the ignition barrel into the cars wiring harness i love how he has run two wires instead of one thick one for like 3cms
needless to say my barrell is now soldered into the harness lol