1990 nissan puslar

take off your steering column. look for about 5 to 8 larger wires. about 12 gauge or so. these wires supply power to accessories and such when the key is on. there is at least one if not two wires that will carry a constant 12v+ power. connect your yellow wire from the deck to this. 3-5 of those wires will show power only when the key is on. one or two of these will show power when the car is on and cranking. use the one that only shows power when the car is on. connect that to your red wire the "accessory" on the deck. that should solve your problem. if possible, run a 16 gauge wire from the battery through the firewall and connect that to the "yellow" constant. it will have proper power and it will sound better.