Amplifier hook up with aftermarket radio
 

05 st 4.7 6 speed,

Installed a new head unit which has been working no problem last two months. I am putting a 200x4 amplifier in for the subwoofer use only, keeping door speakers separate. I have everything hooked up and the amp will not turn on with the remote wire connected to the aftermarket adapter blue/white wire. I believe this is because the stock system was the base model and had no built in amp? should I just connect to an accessories wire for power? All wires, grounds, power cables, fuses are connected.

Well, start with the basics when trying to troubleshoot this. First thing to do is check the fuse(es). If the fuses are okay then try hooking up the power and ground connections directly to a known good battery, and running a wire from the positive on the battery to the remote input wire on the amplifier. This is just a bench test to see if the amp is working at all. If the amp doesn't turn on at that point you have a dud.

The aftermarket radio should have a blue wire coming out of the harness which is the "remote signal" wire. It sounds like you know this already, but that one is simply sending +12v to the amp when the radio is on to turn the amplifier on. That wire needs to be run from the radio to the amplifier separate and is not dependent on the original radio configuration. That is where I am getting a bit confused in your post though as I'm not sure what you mean by the aftermarket adapter... Would that be the plug that comes out of the new head unit?

Re-reading your post I see you put in there that "All wires, grounds, power cables, fuses are connected." Check and re-check this, I can't tell you how many times I've hooked something up only to spend a few hours troubleshooting a stupid mistake I made in the first five minutes. If the wiring is all hooked up properly and the fuses are okay you can check with a digital multimeter your power inputs. Assuming you find good 12v there I'd turn on the radio and check the power on the remote terminal for 12v. If the amplifier is good and the fuses are good this is simply the only place left to find an issue.