if its aftermarket, there should be a blue wire from the back. make sure you don't mix up the REM output wire with the antenna wire, or your amps will only turn on when you turn on the radio, lol.
for a stock unit. you'll need to hook a wire in the fuse box and put a switch on it so you can turn the amps on and off via switch. there is no REM wire on a stock unit.
or you can just find a spot that has power with the key on only and hook to there. itd be easier than the switch cause u might forget and leave the amp on.use a test light to find which one to use.