2003 Mazda B2300 Standard Cab. Manual crank windows and no power anything.
There are no speakers, and no wiring, in the rear panels (behind the seats) unless somebody installed it after the truck was mfg'd or you had a premium sound system from the factory.
The correct size is 6 x 8 speakers.
The nearest point of contact for the rear speaker wiring is under the drivers seat and rubber floor mat; and is the preferred location for splicing into the wiring.
1. Remove the Manual Crank Door Handles:
I noted a lot of confusion with this procedure. On the 2003 Ranger/B2300 the window crank handle does not have a spring clip as shown in many videos, posts, etc., but a torx screw hidden beyond the face cover of the handle:
Use a tool like this to remove the face cover:
And kind of pop that face cover off and then rotate to the side.
There is also a screw in the bottom outside corner of the door panel and another where you grab the door handle. The screws are visible and on the B2300 there were two.
Now lift the door panel up and away from the door frame. The panel must be lifted as shown by how the clips are held to the door:
This will expose the following:
You will note that there is a fair amount of sound insulation already in place so I'm not sure if this hushmat, etc., will do much good.
That black speaker grill is behind the door panel trim and is a part of the speaker itself. I thought about using them in the back panels until I realized that this black grill is non-removable.
I installed Clarion tri-ax speakers in the rear panels and spliced into the speaker wires found under the drivers seat and rubber floor panel/mat.
The bench seat (60/40) comes out with 4 torx bolts and disconnecting one electrical cable. So removal is quite easy and quick. However, make sure that the center seatbelt that feeds through the bench seat is pushed out of the bench seat prior to removal. Otherwise it will tie you up and you could damage your painted surface around the rocker panel beneath the door.
Make sure to use the correct wiring diagram for the year and model of truck before cutting wires. I still splice and solder then use 3M professional electricians tape for the connection. Best audio quality is still through a properly soldered splice.
While you have that door panel off, look inside of the door at your window mechanism and make sure to apply some grease to all moving parts that you can reach. I use Mobil 1 synthetic ball joint type grease but whatever.
Also, look down at the bottom of the door cavity and apply some gear oil to the weld seam area to prevent rust from eating through your door. Oil is great for preventing rust at weld seems.