But you should NEVER connect the amp remote to the power antenna wire on the back of a head unit. Some head units' power antenna signal is only a short pulse, or low voltage, which makes the amp come on and off..... this is not the case all the time; however it can, and has happened.
If the remote wire on the back of the headunit doesn't seem to work right, which can occassionally happen, just run the remote wire into the fuse box. Use the radio fuse, or ignition fuse. This is actually easier, b/c you don't have to run that tiny wire across the driver's feet and have to get up in the dash... from a purely install point of view.