Audio Upgrade

This is a description of the audio modifications that John Tsimaras made to his '98 Grand Prix sedan. He also wrote this page.

It is presented here to provide information to other people looking for similar upgrades. There are some pictures here, but they were taken after the fact, not during the actual installation. You may find this long-winded, or maybe you're only interested in a few sections. This is also my first web page, so if it violates some conventions, please forgive me.

Basically, this upgrade fulfilled my simple requirements:

I thought about it for a while and consulted with a few people as to go about it. Mike Napurano responded to a couple of questions that I posted regarding upgrading the rear speakers. I didn't agree with him at the time, but by the time I finished my research I discovered that his advice to remove the 6X9s altogether was right on the money. Thanks Mike!

The following is a listing of the components that I added, along with some supplies:

Wiring Schematics
So what did I do? I replaced the stock 5 1/4" and tweeter components in the front doors. I also replaced the rear 4" drivers, and as already mentioned, removed the rear 6X9s altogether and added a sub. I also added a 5-channel amplifier to drive the speakers and the sub. I also removed (electrically) the stock amplifier for the 6X9s that aren't there anyway. The reason I did that is that I did not want to have this unit's inputs wired in parallel with my new amp's inputs. I didn't want it to lower the impedance that the stock head unit sees and I was also concerned about it feeding anything back to the head unit and the new amp. Before the installation, I decided how I was going to wire the system. The following two figures show the stock stereo wiring, and how I decided to wire my system. The stock wiring was derived from the Service manual. I strongly advise anyone thinking of doing any significant work on this (or any) car to get the service manual and spend some time planning the mods. This makes for fewer surprises. Original Wiring

The new system wiring is nothing out of the ordinary. It's about as typical as it gets. New System Wiring  

If anyone's interested, I found the following pages in Volume 1 of the '98 Service manual were very helpful: 8A-150-0, 8A-150-3, 8A-201-36, 8A-203-0, 8C-16, 9A-15, 10-6-1, 10-6-11, 10-6-24, 10-10-17, 10-10-22.

Before starting the job, I decided that the line converters and the amp would go in the trunk. I also decided that I would get the signal for the front line converter from under the dash, and the rear signal right from the full range 4" speaker connectors in the trunk for convenience. I also decided to do all the tearing apart first, to get it out of the way so that I could concentrate on the installation once I got started. I began in the trunk. First, roll up and remove the removable carpet in the trunk. I also pulled out the fiberglass spare tire cover. There are some voids under it, and I didn't want to crack it by placing weight in the wrong place. I placed a scrap piece of 1/4" plywood in it's place to cover the hole. I knew that I'd be spending a lot of time in the trunk.

Removing Rear Seat
Next, I pulled out the rear seat. You have to take the seat bottom out first. There are two nylon pulls under it's front edge. They release the front of the seat. I found that they will release easier if you place some weight on the seat directly over them as you pull on them firmly but steadily. Don't tug on them sharply, or they may break. Once you feel that they've released pull up on the seat's front. You can then slide the seat bottom forward and remove it from the car. Once the seat bottom is removed, the seat-back comes next. The seat-back is held in place with four nuts. Two smaller ones about 8 to 12 inches from the side doors, and two large ones near the middle that also hold the inner seat belts in. Take note of the orientation of the seat belts before you pull them out so you can put them back in the same way. Once all the nuts and the two belt assemblies are removed you can pull out on the bottom of the seat-back and move the entire seat-back up to release four wire hooks that anchor the top. I struggled with it for a while, because the bottom anchors kept slipping back over the protruding bolt studs as I pulled up. What helped was the following: Pull out a little on the seat-back until it clears the bolts, and then slip the nuts underneath and thread them backwards on the bolts. The nuts used have washers attached to them, so what I mean by backwards is, have the washers facing out. So when the nuts are in backward, behind the seat, they will prevent it from going back over the studs. You can then concentrate on yanking up without worrying about the seat getting hung up on the bolts. This also makes sure that you don't misplace the nuts until you need them when you put the seat back in. Once the seat is out, the rear deck cover comes next. There are two nylon fasteners on it's front portion that need to be removed. Fortunately, these are not the self-destructing type. Once the fasteners are out, the deck cover can be coached out. You don't need to remove the lower side trim on either side to remove it.

Removing Rear Speakers
With the rear deck cover out of the way, you will see that the speakers are not mounted directly to the metal deck. Instead, they are attached to plastic stand-offs or platforms that hold them about two inches above the metal deck. Unscrew the speakers, but leave the plastic platforms in place. You won't really need the larger ones used for the 6x9s, but you will need the smaller ones to attach the new 4" drivers to.

Removing Door Panels
If you need a second source of information on removing the door panels, there is another document available.  Otherwise, read here:

Next, pull out the front door panels. Start by removing the plastic trim caps that cover two bolts under each door's pull handle. The bolts are torx. I used a hex bit of the right size that attaches to my screw gun to take them out. By the time I finished the job I misplaced the bit and had to improvise in order to put the bolts back in. I found that the flat blade on one of my electrician's screwdrivers was the perfect size to fit in the torx recess. Once the bolts are out, you can start yanking on the edges of the door panels to remove them. As many have said, the nylon fasteners that they used on this car are self-destructing. I was somewhat prepared as I went to a dealer ahead of time and bought a bag of them (10). That's all he had. These are much better than the original ones. The part number is 10153057. Unfortunately, I found out later that each door panel requires eleven of these things, and I only had 10. Before you can pull the door door panels off altogether, you need to disconnect some wires. First disconnect the connector that goes the courtesy light near the back of the door. That's relatively easy. The tweeter connector is also pretty easy. More difficult are the multiple connectors that go to the window and power lock and rear-view mirror controls. The manual says to push forward on the entire control panel, and to pull up on its back end. I tried this, but it didn't budge, and I didn't want to take a chance on marring the door panel or breaking the control panel. Instead, I reached under the door panel, and pushed on the locking tab that held the control panel in place. Much easier. Once the control panel is up and loose, disconnect all the electrical connectors from it and put the control panel itself in a safe place. Once this is done, you can just pull away the door panel and put it in a safe place.

Removing Carpet retainers
This was the easiest part of the job. The front retainers are each held in place with four screws. Three on the bottom (about 2") and one in the front at the top. The rear carpet retainers look easy enough. There's two screws holding each of them in place, but they're actually one piece with the center pillar trim cover. The manual says that if you pull on the trim covers they will release, but mine didn't want to budge. So I left them in place. I just pulled the longer carpet retaining portion out of the way.

Removing Lower Instrument Panel Covers
On either side of the instrument panel, on the bottom, there's a felt cover that covers up wiring and stuff. These are held in place with those nylon fasteners. The good re-useable type. If you pull these fasteners out, the panels will drop out. Twist the little lights off from each and get them out of the way. Save the fasteners for reuse later.

Making and installing amp supporting panels
Before getting started I made two panels out of 3/4" plywood. These go in the trunk, and attach to the steel framework behind the rear seat-back. I used one panel (right) to attach the amp. I made the other one (left) so that it would look symmetrical. I later attached the line level converters to it. For appearance, I covered them with charcoal colored carpeting that I ordered from Crutchfield. Another benefit to these panels, is that they cover up the foam backing that you see against the seat-back in the trunk. I think that looks kinda cheezy. The diagram below shows the dimensions and outlines of the plywood panels. Plywood Panels for Back of Seat

In making the panels, it was necessary to cut out a rectangular section at the top innermost corner of each panel. This leaves the necessary clearance required for the "hooks" that hold the top of the seat-back in place. If you look at the picture below, you can see the two panels installed on either side of the pass-through opening. Just above and to the right of the two line converters (on the left panel) you can see one of the U-shaped hooks that hold the seat-back in place. Without the cutouts you can't get the seat back in. This photo was taken after the installation was complete. Here, the sub was removed from its bracket in order to show what the panels look like installed and the cut-outs required for the hooks. Normally the sub fires into the pass-through. The coil of wire that you see feeds the sub. I left it long so that If I ever need to remove the sub and throw it in the back seat, I won't have to disconnect the wire.  

View of trunk, Sub out of the way  

Looking at the wiring above the amp, I'm compelled to go back out and dress them up a bit better. From this angle it looks like crap, although you usually can't see them. Here's another angle. In this picture the cut-out required to accommodate the U-shaped hook is easier to see. The black bracket at the top of the picture is the sub's support.

Close up of amp area

Once the panels are cut and carpeted (I used spray adhesive that I bought from a local crafts shop) they are screwed in place from the passenger compartment. The way that the car's frame is, you can only attach the panels at the top edge, and along the outermost side edge of the panel. There is no sheet metal surrounding the pass-through opening. However the panels are small enough, that at 3/4" thickness and secured along the entire top and one side, they are fairly sturdy. After all, they're only holding up an amplifier.

Once the panels were installed, the next step was to attach a platform for the amplifier. What's that you ask? Well, the amp I chose was about 1/2" too long for the place I selected. With the amp resting on the trunk floor, the top of it did not clear this ledge that's just below the rear deck. You can actually see the ledge in the picture above  The U-shaped seat attachment hook comes through the bottom of this ledge. So I built (and carpeted) a platform that would raise the sub off the plywood panel enough so that it would clear the ledge. I tried to find an angle that I could take a picture from to show the platform, but I couldn't find one. Not without removing the amp. So this drawing may help.
  Amplifier Platform

I assembled the platform using glue and screws. When complete, I screwed the platform onto the passenger side panel. At this point the installation was ready for the amp, but I waited until all the wires were run into the trunk before mounting the amp to its platform. The reason for this is that some of the wiring enters the trunk directly behind the amplifier. Drilling holes through the plywood panel and pulling the wires through is easier without the amp in place.

Running speaker wires
The level converters were to be mounted in the trunk with the amplifier. I had already decided for convenience, that I would get the front speaker signals from under the dash by tapping into the stock amplifier's connector. As far as the rear speaker signals, by far the easiest thing to do was to get them right from the connectors that originally fed the original 4" full range speakers mounted in the rear deck.

I tackled the front wiring first. Since the signal for the front speakers were coming from under the dash, it was required that four speaker wires be run. Two speaker wires will take the audio signals from the head-unit to the level converters (I call these input wires), and two wires will take the output signal from the amp to the front speakers (output wires). I also used different color wires for input and output, to make my life a little easier. I helped that I just happened to have two different colors of 16 ga. wire.  I used blue for input wires and black for output wires consistently. I guess I'm a stickler for consistency. I also think that this combination of colors sounds better <G>. Make sure that you have enough wire for the job, because it's deceiving. You will need a lot of wire, as I used a total of about 75 feet.

I also decided before beginning that I would run all speaker wires down the left side of the car, and the power cable that goes to the battery down the right. This will minimize noise pickup on the speaker wires.

For the input signals, the most convenient place is to tap them right from the stock amplifier just below the glove compartment. First, disconnect the connector from the amp. If you look at the picture below, find the yellow sticker. Now, if you look just above the sticker, that's the amp partly exposed. The connector plugs into the left side of the amp. Once the connector is free, I cut four wires (there are other ways to tap into the signals, but I was not looking to make a career of this. It is easy enough to revert to the original connections if I ever want to.) You can see the connector with the crimped connectors dangling towards the left, just forward of the center console. The wires to cut are:

Be careful, there's another dark green wire in that connector in position B11. That actually goes to the right rear 6X9. You don't want that wire.

  Stock Amlifier below glove compartment and some new wiring

Before any crimping, I pre-cut two lengths of wire that would carry these signals to the trunk. It's a good idea to wrap some tape around each end of each wire and label them so that you won't confuse left, right, front, and rear. Once that was done, I crimped the new wires to the four wires that I cut from the amp connector. Then run the wires neatly under the dash to the parking brake area. From there you can start tucking the wires neatly where the carpet retainer was removed. I was concerned that it may be very tight to run four speaker wires (2 input, 2 output) under the carpet retainer. I found out that it was pretty easy. You just need to be neat about it. Run the wires parallel and  flat, stacked on top and next to each other. Don't twist them or cross them, and there will be plenty of room. When you remove the carpet retainers you will see a vinyl flap that runs the entire length of the door sill. There's enough room under this flap. If you keep the wires under this flap, you also don't have to worry about the screws cutting them later when you put everything back together. You may remember that I wasn't able to yank the center pillar lower trip piece off. This really wasn't a problem. It's flexible enough that the wires can be pushed up under it. Then continuing past the rear door sills was just as easy. When I got to the rear lower trim (the part next to the seat), I was able to pull that away from the sheet metal. It's held in place with metal re-usable retainers. Pass the wires under this trim piece, and behind the outboard retractable seat belts. It's pretty easy. Once there, I drilled through the driver-side plywood panel and passed the wires through. If you look at the first photograph on this page, you can see the blue wires coming out of the gray panel and right into one of the level converters.

The rear speaker input wires were a piece of cake. Since I bought the 4" Infinitys at Crutchfield, they sent me adapters that plug into the stock GM speaker connectors. I took these adapters and cut off the slide connectors that are used to connect to the speaker itself. I then crimped new wire to the adapters, and ran that wire to the other line converter. When you crimp the new wire onto the adapter, make sure you keep the following convention:

Now that the input wiring is done, it's time for the output wiring. These wires will go from the amp outputs to the new speakers. Again, pre-cut some lengths and label them as before. I ran them from the amplifier area, through the passenger side panel, across the rear seat area, and over to the driver side of the car. I ran these wires the same as the others over to the parking brake area. One wire will go into the left door, and the other will go under the dash, over to the right door. No problem, right? NOT! It's easy enough to get the wires to the vicinity of the doors, but passing them through the rubber boot into the actual door proved interesting. The first one took me about one hour. The second took five minutes, because I learned the trick. What's the trick? Well you have to disconnect the rubber boot from both sides (the door and the frame), and compress it. You can then pass the speaker wires through, one step at a time. First through the frame, pull all the excess wire out. Then thread it through the boot, and pull all the excess wire out. Then pass it through the door opening and finally through the speaker opening. Then go back and push the boot ends back in place.

This assumes that the crossovers for the front woofers/tweeters will be mounted in the door, as I did. If one decides to put the crossovers somewhere else, like under the dash, this will be a little different. You will need to run two speaker of wires through each boot.

The output wires for the rear 4" speakers was trivial. Just run wire from the amp to the openings under the rear deck for the 4" speakers.

Installing Front Woofers and Crossovers in Doors
The woofers were straight forward enough. I first removed the plastic speaker holders (what do you call those things anyway?). I then put a piece of dynamat over each opening (maybe 8" x 12", from memory). I took the cut-out section of dynamat from the speaker opening in the door and stuck it to the inside of the door skin, just opposite the speaker itself. There was already a pad attached there from the factory, so I just put the dynamat on top. When and if you use dynamat, make sure that it stops short of where the interior door panel wants to go. Otherwise, the panel will not sit flush against the door. Once the dynamat was done, put the speaker holder things back in. I also like to put electrical tape over the raw metal edge of the opening so that the wires will not abrade.

I had decided that the crossovers would go in the doors. There is room for them behind a bulge near the bottom rear corner of each front door. Under the courtesy light. I used some pretty sticky pre-formed silicone bead to hold the crossovers in place. With the crossovers there, you need to pass two wires through the speaker openings. One is the main wire from the amp (that came from the trunk) that will go to the crossover input, and the other is the crossover output that will drive the woofer. If you look at the plastic molded speaker holder, there is an indent under the speaker for this, but there's room for one wire only. In the stock scheme, the wires that fed the tweeter passed through this indent. Anyway, I drilled a hole at the bottom of these plastic things, and ran the amp output wire through this hole. This wire gets attached to the crossover input. I then ran another wire from the crossover's woofer output and attached it to the woofer. Place the woofer in this plastic holder and let the wire sit in the pre-formed indent. Otherwise, the speaker won't sit flush. Next connect another wire to the crossover's tweeter output. The other end of this wire should be long enough to reach the tweeter, with some slack. It should also have connectors that can later mate with the tweeters. Take some time and dress up the wires. Tie them together and out of the way so they won't get damaged when the door panel is replaced later.

Installing Tweeters in the Door Panels
First remove the old tweeters from the sail panels in the door panels. There are three locking tabs that hold each tweeter in place. Besides that, there are two positioning tabs that define the orientation of the tweeters. There was no way for me to retrofit these five plastic tabs to hold my new tweeters in place. I broke all five off, and was left with a flat plastic ring that the tweeter could sit against. I tacked each tweeter in place on this ring using hot melt glue temporarily, until I tested them later.

Power Connections to the Amp
At this point, I wanted to start testing my work so that I could start closing things up, so the power connections for the amp came next. First of all, the Grand Prix has a remote 12V power point that is excellent for running a power cable. The picture below shows this point.

Amplifier power cable connection to remote power point

The red cable is the power cable. Note the fuse housing on the power cable right by the rear strut tower bolt. You will also note that the power cable is wrapped around an existing cable. I did this to make sure that it would not touch the hot engine. One of these days I will dress it with wire loom. Connecting to this power point was the easy part (But don't do it just yet. You'll want to run it to the trunk first or you could have some pretty sparks. It's best if you attach the other side first, the ground cable, and the remote turn-on lead before you attach the power lead to battery). The not so easy part was finding a way to bring the cable through the firewall.  I found a soft rubber grommet behind the engine where a cable was already going through. It looked like a great place. It's shown in the picture below.

Power cable passing through firewall

In trying to push the cable through the rubber grommet, I discovered that there is a rubber sound deadening membrane on the compartment side of the firewall. So I couldn't push the cable through. I took a long screwdriver, and gently <G> passed it through the grommet, and then pushed it through the membrane. I left the screwdriver in place to help me locate the new opening from inside. Once I found it, I enlarged the hole a bit. Then it was simply a matter of threading the cable through the grommet and the opening in the rubber membrane on the inside. I would recommend that you seal the area in the grommet where it was violated <G> with some silicone. The picture above doesn't show it, but I have since sealed the opening. Once the cable is through to the inside cabin, it's an easy matter to run it down the right side of the car to the amp in the trunk.

The ground wire was much easier. I connected it to one of the screws that hold the sub bracket to the bottom of the rear shelf.

The only wire left to do before any testing was the remote power lead. This wire turns on the amplifier when it receives a 12V turn-on voltage. This is usually a much thinner wire than the power and ground connections for the amp, since it draws very little current. It's typically about 18 ga.

I have the UP3 stereo (CD in dash) with the rear-window antenna. The presence of the rear-window antenna makes it very easy to get a turn-on voltage for this lead. The wire to tap into is the yellow lead that goes to the antenna amplifier. It turns out that the antenna amp needs the same turn-on voltage to do it's job. The bonus is that this lead is also hot when using the CD. (I cannot speak for other stereos, or for cars with the mast antenna. If you don't have the rear-window antenna, you may have to get a signal from the instrument panel fuse block)

Anyway, where is this wire? I took a picture and had intended to include it here, but after looking at it I decided that it was hard to make out and would probably add confusion. So I left the picture out. The place to look is under the rear shelf, on the passenger side, somewhere between the 4" speaker opening and the right-rear strut tower. You will see a bundle of wires (portion of the rear deck and trunk harness) that is taped over it's entire length with black electrical tape. At one point the bundle splits and most of the wires continue on under the deck, but a smaller grouping separates and goes up into a hole (about 1" in diameter) into the rear deck. It's easy to identify because one of the wires that break off and passes through the hole is a much thicker black coax lead. This is the antenna lead itself. One of the wires accompanying this coax is yellow. Be careful, because there's another yellow wire in the group of wires that do not pass through the hole. MAKE SURE TO USE THE ONE THAT GOES THROUGH THE HOLE. Now, there's only about a 2 inch section of it exposed, so you may need to cut back some of the electrical tape that's used to bundle the wires, just to have some working room. Tap into this wire using your favorite means. I used one of those T-connection connectors that I bought in an auto parts store. It caused me some grief, but that's a story for another day.

Connect the RCA wires between the level converters and the amp inputs, and you can start your testing. At this point when you turn on the radio the amp should also turn on, and you should get sound out of the front door woofers. The tweeters should not be in at this point yet. Make sure that the balance and fader controls aren't crossed. If you labeled the speaker cables as you ran them there shouldn't be a problem. You could also listen for the speakers being out of phase. Out of phase speakers have a very distinctive sound. Basically, there is no imaging as it's hard to localize where a sound is coming from.

Installing the Tweeters and door panels
At this point the tweeters are tacked into the sail panels temporarily (with hot melt glue), and the wires leading from the tweeters should have connectors that will mate to the leads coming off the crossovers. Pull the door panels over to the doors and connect the tweeter connectors to the tweeter wires from the crossovers. Turn on the stereo again and make sure that the tweeters work. Once the tweeters were tested and they worked, I used some more of that pre-formed silicone bead to secure them in place inside of the sail panels. The hot-melt glue that was used to hold them would likely fail in the summer as the interior gets real hot when the car sits in the sun. Now I was ready to close up the door panels.

I've mentioned already that the nylon fasteners are not really re-useable. But I only had 10 of the new ones to use between the two door panels. So, I discarded the five sorriest looking fasteners from each door panel. I then moved the fasteners around so that the new ones were in the more "strategic" locations, like the tops of the panels, the bottom corners, and one on the bottom edge in the middle. Putting the door panel back in is pretty easy. Just reverse the steps used for disassembly. First pass the door release handle through the panel, align the panel in it's general location, reach in and connect all electrical connections (to the courtesy light, and to the switch control panel), and push the panel back in place. Don't forget to put the torx screws under the door pull back in, and the trim caps.

Installing the rear 4 inch speakers
This is one of the easiest steps. You need to run the speaker wires from the amp outputs to the holes where the 4" speakers will go. Connect the wires to the speakers and then mount the speakers to the plastic platforms. Done! Now test the rear speakers as well.

Installing the Sub
The sub that I used was a breeze to install. The sub mounts to a steel bracket that attaches to the rear deck from underneath. I actually installed the bracket earlier, when I did the power connections. I had decided to attach the ground cable to one of the sub bracket mounting bolts, so I had to install the bracket before I could power up the amp to start testing. There was no science here, I just decided where the bracket goes and screwed it in place with self-tapping sheet metal screws. Before I attached the bracket however, I did cover a good portion of the bottom of the deck with dynamat. I attached the wire to the sub (12 ga.), and then the sub to the bracket. That's it!

It's worth mentioning that my amplifier and configuration does not require a separate input signal into the amplifier for the sub. The amplifier generates the sub output signal internally from the other 4 channels. (Another reason that I did not need to reuse the stock amp.)

Finishing Up!
Once I was satisfied that everything worked, I put the carpet retainers back in, vacuumed, put the rear-deck cover back on, and re-installed the rear-seat and seat belts. Don't forget to go back in the trunk and dress the wires up a bit for a neat appearance. Here's what my trunk looks like.

Trunk view of completed system  

The wires near the top usually don't show, they're really far back and under the rear deck. Man, what a difference over the stock system. This was a long and tedious process but well worth it! If anybody cares, I spent two very full days doing the install (about 20 hours). This was preceded with another 5 - 8 hours in the shop building cables, making the panels and platform, and covering them with carpet.

If you have comments or questions about anything on this page, please read the follow-up pages:

Audio Follow-Up #1
Audio Follow-Up #2
Audio Follow-Up #3
Audio Follow-Up #4
Audio Follow-Up #5
Audio Follow-Up #6
Audio Follow-Up #7

and if your questions are still not answered, e-mail John Tsimaras and ask!