My pioneer deh-p5500mp Car Radio
hmm.. thats a nice radio, not too shaby heheh...
Well your car radio should have a Blue wire with a white stripe for the remote, in case you are interested in the user manual (wich im guessing you dont have)
it has a diagram of the harness and it shows a blue/white remote wire, so im guessing that you bought it used and probably got a different harness with your car radio... but then again thats too weird
you could do a check to see if thats really the problem... just feed 12V From the power terminal of your amp to the remote terminal, that should turn your amp on and you should be able to listen to your car radio's output (id suggest not setting the volume all the way up when doing this XD)
Hope it helps