Does the truck have the stock amplifier? I'd imagine you did, but have you double checked that you've got the in and out going the right way?
The remote wire is what turns the amp on, it needs to be connected. Finally, that "amp" really isn't meant to be used like that. As best i can tell there is really no gain (aside from a hi/lo switch) or adjustments on it, so you have no way to tune it properly to your system. It's quite likely if you have the basic ford HU it puts out less power than the Alpine HU, so you would need to be able to turn the gain up on the amp to get the same output.