I'll get straight to it, the only way I can get my radio to work is to wire the 12v constant (yellow) and the 12v acc (red, maybe yellow and red constant) together. I have tried wiring yellow to red and red to yellow but nothing. The idiot that had it before me had a blue tooth wired in there with the constant and acc together. That was fine for me at first as I drove my z everyday, but now as a weekend car, I drive it only on sunday as thats the only day i have off, and the battery is dead after 2 days of not being started. I read what I could and found a couple different answers but not anything i know how to do. If i cant figure it out, its going to cartoys

 

Red (ACC) and Yellow (constant) should never be wired together...
That basically is telling us that the BT unit is powered on even when the car is off. No wonder the battery is dead every weekend...

If I were you, I would use a DMM (digital multi-meter) and check the voltages on the constant and ACC line. Constant should have 12v at all times, and ACC should have power only when the ignition is turned on (1 click, or car running).

Are you trying to power a stock radio or aftermarket?
If aftermarket, was it wired properly using a harness that plugs into factory, or was the factory plug cut off and new radio wired directly?

My guess would be that the ACC fuse is blown, and the previous owner tied the BT units ACC line to constant to get it working. Check all of your fuses.

Additionally, a picture of the harness in its current state would probably help troubleshoot. I have seen some really horrible radio harnesses in my time that can be made 1000x better with a soldering iron, heat shrink, and some zip ties.