amp turn on wire in nissan altima

I have a 97 nissan altima that I am working on.   before I remove the factory HU and make a whole lot of work for myself,   does anybody know if the amp turn on wire is there on the original factory harness or do I have to buy an adapter.   the reason I ask is because the antenna trigger wire does not put out enough amperage to even trigger a relay.   so what I want to do is run a seperate wire back to trigger an aftermarket antenna.   If that wire is there it will be great.   I will tell you where it is supposed to be.   on the top of the smaller plug.   thank you      the hot wire -ron

you shouldnt need a relay if you are just going to power up one amp, you can use 12v switch power on the radio harness for your remote turn on for your amp