The first CAN bus trucks were 06. Prior to that they were PCI bus. Check that you have 12v at the radio connector C1, pin 13, dark green wire. That feeds 12v from the radio to the amp at C1, pin 5. If you do, you are missing the bus signal from the factory radio to tell the amp the radio is on.
Depending on how you adapted the wiring you can fool the amp by wiring the factory radio with B+ and ground, and wire the bus from the factory radio to the bus circuit of the truck. Do you have a wiring adapter that will plug into the factory radio? I saw a Magnum that the customer installed the factory radio under the seat with power, ground and bus to fool the amp. The only other solution is to replace the factory amp with an aftermarket.
To clarify you need three powers, 2 B+ (C1 pins 1 and 12 grey/red) and one switched (start/run) B+ (C1 pin 2 pink/yellow)
2 grounds, C1 pin 11 and 22 Black and black/green
The PCI bus is C1 pin 14 white/violet
For ease of this test, you can run B+ (just use B+ for the switched B+ for the test) and ground direct from the battery for all three powers and the two grounds. Plug the bus circuit into the data link connector under the dash to pin 2, white with violet and you can just leave the aftermarket radio installed (except to check for 12v at C1 pin 13 above)
When you turn on the factory radio power the amp should start working.
I know this sounds confusing, but a roll of wire and a spare factory radio connector will make it a ten minute test.