Monsoon amp problem
 

I wanted to buy a monsoon amp cause when I bought my R32 it didn't have one in it. So bought an amp and went to plug it in(the amp has 2 plug spots) and alls I could find was the one green plug but not a second one? So I plugged it in and stereo sounds the same nothing changed..... I don't know if I need that secod plug and if so where did it go? I will say I did notice some aftermarket wires that were cut running up into the side wall but havnt traced them down. So obviously there was... An aftermarket set up but still if their was, then why would I be missing that second plug....? I don't know why it would have been cut or deleted to run an aftermarket set up? But please any thoughts or suggestions please let me know.