What is a compatible replacement for the factory subwoofer?

Remove the door opening weather-strip. Refer to Door Opening Weatherstrip Replacement in Doors.
Remove side sill trim plate. Refer to Door Sill Plate Replacement in Interior Trim.
Remove the lower quarter panel trim. Refer to Rear Quarter Trim Panel Replacement in Interior Trim.
Remove the center pillar upper trim panel. Refer to Center Pillar Upper Trim Panel Replacement in Interior Trim.
Remove the quarter upper trim panel. Refer to Rear Quarter Upper Trim Panel Replacement in Interior Trim.
Remove the center pillar outer applique. Refer to Center Pillar Applique Replacement in Exterior Trim.
Remove the roof drip molding. Refer to Body Side Roof Drip Molding Replacement in Exterior Trim.

Important: It is necessary to use new nuts when reinstalling the quarter window.
Remove the nine quarter window nuts (1), securing the quarter window assembly (2) to the body opening.
Caution: When working with any type of glass or sheet metal with exposed or rough edges, wear approved safety glasses and gloves in order to reduce the chance of personal injury.
Important: When removing the quarter window from the body opening make sure that the attaching pins are clear of the outer body.
Remove the quarter window (2) from the body opening.

Remove the rear seat cushion. Refer to Rear Seat Cushion Replacement in Seats.
Remove the rear seat back. Refer to Rear Seat Back Replacement in Seats.
Remove the door sill plate. Refer to Door Sill Plate Replacement .

Remove the 3 quarter trim panel retaining screws (1).
Starting at the lower edge of the trim panel and moving alternately clockwise and counterclockwise, pull outward on the trim panel to disengage the eight rear quarter trim panel attaching clips (2).
Remove the quarter trim panel from the vehicle.
Remove the 4 radio speaker grille speed clips (1), securing the speaker grille.
Remove the speaker grille (2).
Remove the rear quarter trim panel insulator (1), from the back of the quarter trim assembly (2).
Remove 7 rear quarter trim panel armrest retaining clips (1).
Remove 7 rear quarter trim panel armrest retaining nuts (2).
Gently pry the quarter trim panel armrest insert assembly (3), away from the rear quarter trim panel and remove.

You mite look for a video on youtube !

That is a fuel vapor box for emissions.

no problem with replacing all speakers with ones that are compatable wth you new amp .. and that means the the speaker impedance has to be wtihin the range of what the amp can drive (like 4 ohm, 8 ohm, 16 ohm) .... the subwoofer needs inputs from both left and right channels .. it also needs its own amplifier and low pass filter .. this all may be built into your after market amplifier .. if so you will have an output marked sub (that will directly drive the subwoofer) .. or you may have a low level outdput marked sub that goes to your subwoofer amplifier if it has one .. .. sometimes the woofer has its own built in amplifier and filter .. it then just needs power and inputs from each channel .. since you are running 500 watt speakers, they likely already have a subwoofer component .. (speakers that extend down to 20 hz or lower .) if so, you may not need an additional sub-woofer .. just make sure all the speakers are phased correctly .. (wired to work together not fighting each other ..) .... an amplifier capable of driving 500 watt speakers can draw peak currents that are very high .. so power wiring would have to be very heavy and preferably go directly to the battery with an inline fuse right at the battery ..

It should be mounted on the passenger back. you will have to remove the rear quarter interior panel, The trim where the hatch locks and around the trim where the hatch meets the rear. once the trim is removed you can access the sub, it is bolted to the car and plugs into the factory amp, which is located right in front of the sub. After taking the bolts out, the sub will come out.

i would get a reprint from the ford service manual,before bending the subwoofer frame.it will only cost a couple bucks and expose the dark secrets that ford come up with

Section 15-03: Speakers 1997 Villager Workshop Manual DESCRIPTION AND OPERATION Radio Speakers All vehicle sound systems are equipped with radio speakers (18808) located at all four corners of the vehicle. The radio speakers are mounted in the RH front door (20124) and LH front door (20125), as well as behind the quarter trim panels (31012) in the rear of the vehicle. The Ford Super Sound Audio System has the addition of a subwoofer mounted in the RH quarter trim panel.
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Radio Speakers, Front Door Removal

1. Remove the front door trim panel (23942). Refer to Section 01-05 .
   

Trim Panel(s), Door Front
Removal

1. Disconnect the battery ground cable (14301) if equipped with power locks or power windows.
   
2. CAUTION: Use care when removing the front door inside handle escutcheon (22620). Failure to do so can result in damage to the component.
   Carefully pry off the front door inside handle escutcheon by inserting a standard 1/4 inch screwdriver between the top rear portion of the front door inside handle escutcheon and the front door trim panel (23942).
   
3. Remove the three cover caps and front door trim panel screws.
   

1. Remove the one front door trim panel capped screw from the door pull handle.
   
2. If equipped with power windows, remove the door pull handle. Disconnect the electrical connectors.
   
3. Slide a flat-bladed tool behind each of the retainers and twist the tool to disengage the front door trim panel from the front door (20124).
   
4. Remove the front door trim panel.
   

Door Electrical Connections
Removal and Installation
Refer to Section 01-11 for Power Window, Section 01-09 for Power Mirror, or Section 01-14B for Power Locks. Watershield
Removal

1. Remove the Front Door Trim Panel . Refer to the removal procedure in this section.
   

1. Remove the front door watershield by carefully detaching it from the adhesive.
   

1. Remove the four front door radio speaker screws.
   

It is a tedious task, however simple if you have patience. In order to get the sub woofer out, you need to take out the paneling and floor in the back. Start with the plastic knobs near the rear hatch door and then pull the floor back and the panel with the cup holder. I believe i needed to take back the panel on the inside of the rear pillar as well. Everything snaps back in place, so it is not a big deal. Just don't force anything so that you don't crack the plastic. The subwoofer is mounted from the back, so that is the only way to actually get to the hardware holding it in place. Otherwise it will just spin and spin if you try from the front. i replaced mine about 2 years ago with an 8" Kicker, however i think the factory sub had better sound. The amp is designed specifically for that sub. However, it did blow out and the kicker gets the job done. Good Luck!!

I would be very proud of that truck as the sub that came with the truck was only a 8". The only one that works is the factory model as it is a 1 1/2 - 2 ohm speaker; replacements are 4ohm. You will have to replace the amp as well if you put in an aftermarket sub. Oh and apparently the amp will have to have "speaker level" inputs as opposed to pre-amp inputs. I have a 1999 Eddie Bauer wih a blown sub and I'm trying to decide what to do as well. The speaker is $400 with tax in Canada! Good luck.

There is a lot involved in replacing these speakers. You should also know that the original factory speakers are 10 ohm speakers. This means that if you replace them with new speakers (most of which are 4 ohm) you run the risk of damaging the stereo, the speakers, or both. This can also cause a potential fire hazard in your car. If you want new speakers, you really should look at installing a new stereo as well.

To get to the back speakers, you will need to remove 2 bolts located under the front edge of the rear seat (bottom). After you remove the bottom, you will need to remove the rear seat (back). This involves removing the bolts that hold down the rear seat belts, which is a large sized torx bit (T-45, T-47, or T-50... Don't remember which). After removing these, lift straight up on the seat back to remove. Now remove the deck brake light housing, and the bracket that holds it. Now the deck cover can be removed. Be careful not to bend it too much getting it out from under the side trim on both sides.

For the front speakers, you must disassemble a good portion of the dash. Remove the screw holding the light switch and the wiper switch housings. This screw is underneath each housing. Once removed, there are dash mounting screws behind them. These screws (and many of the other dash screws) are a smaller torx-bit (T-10 or T-15, don't remember which). Sometimes they use a 7mm bolt. There is a cover panel just above the glove box. This panel is held on with 2 screws located in the glove box. After removing this panel, you will find 2 or 3 bolts holding on the dash. Last but not least, you will find 2 bolts inside each of the defroster vent grilles. These grilles just snap out for easier access to the bolts.

1991 Pontiac Grand Am Car Radio Stereo Audio Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger: Pink
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 4" Round
Car Audio Front Speakers Location: In Dash
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: 6" x 9" Oval
Car Audio Rear Speakers Location: Rear Deck
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue