Trying to replace the single din & cd player with a 6 disc 39100-S84-A300 from a 2001 Accord. I do not know what to do about the SCTY wire?

 

BLU #4 goes to the passenger side multiplex control unit. Diagnostics for the BLU wire are there should be less than 1V to ground. From my understanding this is a communications wire and not a power wire.
Passenger side multiplex control unit is used for a few conveniences, such as allowing the radio and windows to work for a few minutes after the key has been turned to OFF and the doors are still closed.

Have you tried wiring up the system and seeing if it functions correctly without #4 BLU? What are you dong with #19 RED?

 

Just leave the security input wire disconnected. On 6th generation Accords with the OEM security system, when the audio unit is disconnected the alarm will sound. Essentially, that security input wire loses its ground and the input voltage goes to 10 volts; and the alarm sounds.

 

Thank you I will try that.