question about car stereo and amp.

So i just installed a new head unit (JVC KD-HDR50). I had a (Sony Xplod CDXGT520). i noticed that the plug in for the sony fit inside the back of the JVC so i just used that plug in. Everything works great but im not getting power to my amp. I grabbed my voltmeter and checked the amp its got power to the 12v the ground is solid but there is no power going to the blue wire at the amp. IS there supposed to be or not. There are no fuses for the blue wire it runs from the head unit direct to the back and then to the amp. I checked all of the fuses amp has 2 those are good and the main fuse under hood is good and has power. What did i do wrong? did i need to use the wires that came with the JVC even though everything works great>
thanks for you help guys.

You got lucky that you did not blow up the new radio. I would look at the manual that came with the new radio and see if the blue wire is in the same place as the old radio. You might have to use the new radio wiring harness. I use to do car radio installs and have always used the new harness that came with the new radio.

The blue wire is your signal wire, right? If it's what I'm thinking it is, it should be on (live) if the head unit is on.

Yes that is what the blue wire is for or it can be used for the auto antenna also.

He is very lucky he didn't let the smoke out of the output IC chip in the new deck by using the old sony wire harness.