I'm not sure. I just got tired of chasing it. I did some searching to see if I could find a power amp plug adapter of any kind that went from the factory harness that plugs into the amp, to ANY aftermarket amp. I didn't find anything. That doesn't mean it doesn't exist, but it does mean you'd have to probably contact a good stereo shop to find one if they do. I think the guy here could see that he was going to have to actually do some work to make it happen and he decided it wasn't worth his time...

Look up the wiring diagram for the power amp harness and you can probably figure out which connections can be re-used. Make a harness to go from the factory harness to your replacement amp using the right connections on each end and you could avoid cutting your factory harness or duplicating speaker wires. Do the same on the head unit side and you could avoid cutting there. Some of the factory leads may end up unused.

Check the rest of the forum here - there seem to be plenty of stereo upgrade threads and I am sure tid-bits can be found about all this.