I just ordered a Pioneer DEH-P7500MP to replace the original factory hu in my 2003 Explorer. The system being replaced is the Audiophile version.

Here are my questions:

What sort of wiring harness do I need? I saw a Scosche FDK9 that needs to be used in conjunction with Scosche FAI-3. What exactly does that second part do?

I thought the original hu powered the front and rear speakers with an internal amp and that there is a line out to the factory amp for the subwoofer. Am I going to be able to drive the speakers with the Pioneer's internal amp and send a lead to the factory amp for the sub?

I will eventually be replacing the front speakers with MB Quart 5 1/4's and will use the line outs to an amp to drive them. Should I replace the rear speakers at the same time? If I do, will it be ok to run them off the Pioneer internal amp, or should I look into getting a four channel amp instead?

Are there any good four channel amps that will power 4 speakers at about 75 watts each for around $200?

Any suggestions are appreciated.

 

Here is an example for an amp. Kicker
There are alot of 4ch amps out there. Most 75x4 are in your price range.
As far as the radio, do you have the DVD system? Your radio has 3 plugs behind it. One powers the dvd and one powers and controls the cd the other is the main plug and largest of the 3. It has the power and speaker outputs from the radio. I wrote the colors down at home of each of the main wires if you need them but with the harness to an after market radio you probly dont. I am not sure if the audiophile system uses an external amp for the speakers because I cant find it and i know from test the speaker outputs from the radio, that the radio is putting out decent power. I use an old Polk audio 5.25 speaker from an old component set I had and the radio puts out a bit of power. The stock sub amp is on the sub enclosure and that uses speaker wire input but I didn't trace the radio wires for it because I'm not going to use it for my system upgrade. Unfortunatley I cant replace my radio because of the dvd. I have the Pioneer 7300 The model you have replaced mine. Pioneer make nice radios and they sound real good once you get the eq set right. Ok back to your question,...... if you have any doubts about the stock amp you can run your own wiring. I would say go with 18-16ga from your radio to the speakers. It is very easy to do except for the driver side door. You will have to remove the emergancy brake bracket then its easy to push thru. The front speakers on the audiophile system sound unbelievably nice. They are 5" components.

 

You might need the Ven 4.5
If it does have an external amp.