I have an aftermarket competition Clarion HU which I installed and I connected the remote wire from the stereo to a switch and then to the amp so I can shut the amp itself off individually if needed. The factory amp I attached to the power antenna wire as mentioned earlier, the power antenna wire from the stereo will be a constant power wire when the HU is powered on, just like the remote wire on almost all HU's newer than 2000, as well as many of the older ones as well. However some of the older models as mentioned above will only have power when you have the HU switched to AM or FM reception, I have only experienced this once in the past though. Watch the plugs on the old Tahoe trucks though, as things age they start to fall apart a bit and malfunction, the wiring harness to my factory amp had the pins pulling out of the plastic plug and they needed only to be pushed back into place for all the connections to work properly.