Er, one thing I forgot to mention, and really need to, is that the replacement Pioneers I used are 4 ohm speakers, and the originals are 13 ohms. What this means, in a practical sense, is that plugging these 4's into the connectors the old ones plugged into puts them in parallel with the front door speakers.
With the change of impedance, there is a shift of the percentage of power delivered to the dash and front-door speakers. No longer is the sound balanced properly - the speakers on the dash will be too loud, and the ones in the door will have the power to them reduced. (Don't worry about how this works, just trust me that it does, and that it can even be proved from the schematic.)
So, what does one do?
One needs to put about 7 to 9 ohms of resistance in series with the dash speakers to re-balance the system.
I prefer the sound to have a little more 'presence' and for the dash speakers to be a little more obvious, so I picked up a couple of 10 watt, 6.8 ohm resistors at Fry's Electronics. (If you want the dash speakers to be a little more muted than that, use 8.2 ohm resistors - that will make their level match the OEMs pretty close.)
I glued my 6.8s to the back of the speaker magnets and hooked 'em up between the speaker's hot lead and the red lead from the speaker connector I ripped off the OEM speakers.
If you don't do SOMETHING to reduce the level of the dash speakers, they will be much too loud and the door speakers will be almost unheard.
Hope this helps!!!
Tomas
P.S. I'd totally forgotten about the resistors I added until I just took one of the dash speakers out to find out what was 'buzzing' behind it - one of the resistors had come adrift - I hadn't glued it down quite well enough and it was vibrating against some underdash plastic. Trust me, it WILL NOT come lose again.
T