Zapco AG650 Amp clicks on and off and doesn't want to "turn-on"

I need your help. I have a Zapco AG650 Amp that I am looking to replace a DEI 1200.5 Amp in my current car audio system. The DEI 1200.5 currently works, but the AG650 does not. The following is the equipment that is installed:

Alpine 7815 Deck
MB Quart Separates in the front and back
2 - Digital Design 10" 4 Ohm Subwoofers
4 Gauge Power and Ground
No Stiffening Capacitor in the system
Monster Cable interconnects
125 Circuit Breaker 8" away from the Optima Yellow Top Battery
Installed in a 98 Honda Accord

The question I have is that upon installation of the Zapco Amp, all it does is keep "clicking on and clicking off" once it was hooked up to the power, ground and remote wire and the deck was turned on. The 3 fuses on the exterior of the amp are not blown after pulling each one and visually inspecting them. The amplifer was then connected to an external 120v A/C to 12-15 V DC power source to see if it would turn on after the amp didn't work. But no change to the amp, it still continued to "click on and click off." A suggestion was to move the ground wire. However, after testing it with an external power supply and the original amp continues to work after it was re-installed, I have my doubts...but I'll give it a shot...is there any other suggestions that may have been overlooked? Or is the amps power supply not working? Any help to solve this problem would be greatly appreciated. Thank you for your help.