Some easy things out of the way, in case you didn't do them yet...

On the side where you plug in your inputs, make sure the button is pressed in to receive a "hi" input level (speaker level). You'll also need JUST a cable that goes from speaker wire to RCA, not a signal converter. If you have a signal converter then try it on the "lo" input setting, but this amp might not like it.

Also, are you sure you have the correct two speaker wires (spliced close to the factory speaker rather than somewhere in the middle where you can't verify the ends)?

Since you're using high-level inputs (if no converter box), have you tried wiring it just to turn on via the input signal (DC offset they call it) rather than with a 12v signal wire? If you're getting a green light then it's on.

Those are my first thoughts at the moment.

-Rog