1991 mercury sable

I have a '92 Mercury Sable with Ford Premium Sound. I didn't realize It had the PS until today. I tried to install a Pioneer AVH-P5700DVD head unit, everything works like a charm, except no sound. Now I just went through the same thing with my '03 Tiburon, I had to tap into the factory amp and voila! Music.  Well, the same does not apply for the Sable. I can not find the Amp trigger wire. I was doing some searching online and found a harness needed to bypass the amp, but I would rather not bypass it. So I guess my question(s) would be, can I just tap into it like I did for the Tiburon or do I need a whole new harness? I tried searching the 2 car side harnesses to see if I could locate the Amp trigger wire somewhere... no such luck. I have a feeling I am going to need to rewire the whole head unit again and get a new harness. I know the bypass harness is the 70-5514 I could use the metra numbers for the opposite. Or even instructions on how to just tap into it like I planned on doing. Which ever is easiest. btw, the sable is wired with a hard wire, (no splicing or cutting original harnesses) I bought an open end harness and soldered them because I can use a smart harness on the DVD head unit.

IN CONCLUSION. I guess I would just like to know if it is possible to just tap into the amps with the wiring I have done already, if not. What is the harness that I will need?

Thanks

-Rev