2004 grand marquis to 97 ranger

I recently install a radio with cd and tape from a 2004 grand marquis into my 97 ranger. I wired a new harness correctly. when I turn up the volume a little past half way the sound begins to distort. When I turn the volume below that mark it sounds perfect. When the bass hits hard at half level the sound does the same thing. I have the wiring digram for the marquis.. There is only two connection I didn't do according to the diagram. One is to the VSS and power during start. Do any of these matter or is there something else I need to do get the new radio work with my older truck system.

meant to say 2003 grand marquis...sorry about the typo

Well, in my experience, that's usually where Ford radios distort- around half volume.  However- I wouldn't say it sounds perfect below that.My ex once told me I have a perfect face for radio.

the sound goes in and out like it needs more power