Certified World Wide Website


2004 Chevrolet Blazer ZR2





Wired for Sound



In December 2004, I was getting to know my new Blazer, the sport-utility I thought I'd never own. These vehicles were in the process of being phased out of production after 20 years or so as a staple in the Chevy lineup. Even in 2004 they were old school, in an unsuccessful bid to keep up with rapidly changing technology. My Blazer came with a fancy (at the time) in-dash 6-disc CD changer, but no auxiliary input for my MP3 player. I had reached the point in my life where carrying stacks of CD's inside my vehicle was just not going to happen, so Plan A was to connect my MP3 player to an adapter which plugged into an unused port on the back of the head unit.


Plan A quickly expanded into a Kenwood KAC-8401 4-channel amplifier and 3 pairs of speakers to upgrade the stockers. Now we're talking. And while I was at it, I'd add an Infinity BassLink powered subwoofer to pump out some bass.


Plan A was scrapped when the auxiliary port didn't work. I moved on to Plan B, which was adding a Sony CDX-F7700 head unit with its own auxiliary input and internal amp. I installed all of these things and the new sound was great. Then I realized that when the door and dash speakers are wired together in parallel, the ohms went from 4 to 2. This was not good for the amp in the head unit.


I moved on to Plan C: Use the Kenwood amp to power all 3 pairs of speakers. Its four channels were capable of handling 2-ohm loads and it pumped out 60 watts RMS versus the Sony's 23 watts RMS. But where to mount the amp? It was too big to fit under any of the seats, and I didn't plan to have it lying in plain view of would-be thieves. Also, I wanted to retain all of the limited cargo space in the back of the Blazer. I'd read about amps being mounted inside the small storage compartments behind the front seats, so that's what I did. It wasn't easy and it took some time, but the project worked out well.





Above is the finished product. This and the Infinity BassLink were the only visible components of the sound upgrade. To get to this point required time, patience, and lots of research.



the project





These photos below illustrate most of the steps for completing the sound project.



Project Underway



The first step in this project was to remove the rear seats and trim pieces around the doors and interior. The Kenwood amp was too big to fit under the seats. I found an alternative.



Creating Amp Space



The area under the speaker grille was just large enough to fit the amp. I had already removed the plastic storage compartment, exposing the inner bodywork behind.



Modifying the Lower Body Panel



This is the lower interior body panel which was removed to mount the amp. The panel contained cupholders and a small door. Behind the door was a small storage compartment (covered in gray foam insulation).



Modifying the Storage Compartment



Above is the body panel with the storage compartment removed. The compartment was joined to the panel with plastic rivets. The access door is visible on the right.



Preliminary Amp Mount



The amp wasn't a perfect fit, but close enough. I used a Tsunami amp wiring kit for the Kenwood amp, which included the 4-gauge ground wire and the blue 8-gauge main wire to the battery.



Storage Compartment Re-installed



The amp fit perfectly in the storage area. With the plastic compartment removed, it actually opened up the space a gave more room for storage. I was somewhat concerned with the lack of airflow to the amp, but it never overheated.



Head Unit Install



Hard to believe all these wires fit inside the dash. It was a tight fit.



In the side door



Passenger side door with panel removed. Note my stellar duct tape job securing the crossover for the Infinity Kappa 62.5i speaker. Duct tape has a useful life of about 5 years. After that, things start to rattle.



BassLink



Here's the Infinity BassLink installed in the rear passenger-side cargo area. It didn't make my hood bounce, but added enough bass for me. Most of the cargo area was preserved with this setup. The sub was built well and held up to a fair amount of abuse. The internal amp eventually failed in 2011. By some stroke of luck I'd left just enough space between the sub and the interior wall to fit a small mono amplifier to power the speakers externally.





Failed sub amp



When the amp failed, I pulled out all the internal electronics and powered the subwoofer externally.



Sealed back up



I like the tight sound of acoustic suspension bass, so I sealed up the openings.



Separate sub amp



I chose a Pioneer GM-D8500M mono amp to
power the sub. It was reasonably priced and
compact.



Sub amp mounting



The amp fit perfectly behind the sub, screwed into the side wall. All the wiring was already right there.



Distribution block



I had already added train horns, which came with an air compressor. With the addition of the sub amp, yet another fused power wire was needed. Now with 3 wires connected directly to the battery (power amp, subwoofer amp and air compressor), it was time for a fused distribution block.



Through the firewall



I ran the battery wires for the Kenwood amp (blue 8-gauge) and the sub amp (red 10-gauge) through the radio antenna entry point under the passenger side dash. I was able to stuff the smaller red wire
through the same hole as the antenna wire, but the blue wire needed its own hole and grommet



Preserving the steering wheel remote controls





PAC SWI-X



This device allows an aftermarket head unit to be operated by the steering wheel controls. The concept is pretty simple - it takes the signals from the steering wheel controls and matches them up with IR signals from the Sony remote control. So it's basically a learning remote. Installation is a little complicated to figure out at first, but eventually I got it right.





The SWI-X install can only be done with the radio out of the dash, so installing it while you're doing the head unit works better. The first step is figuring out which wires in the factory harness are responsible for steering wheel controls. The Blazer uses a GM24 wiring harness, as identified in the Vehicle Connector Chart in the PAC instructions. In the Vehicle Application Guide, the location of the steering wheel control wires are listed as pins A6 and A7.


Pin A7 is a blue wire that carries the steering wheel control signals. Pin A6 is green wire that is the 12V power wire which gives the steering wheel controls the juice needed to operate. The Crutchfield wiring harness I got for the Sony head unit doesn't supply power to Pin A6. So I cut the green wire and hooked it into the switched 12V main power wire. That way, the steering wheel controls got their 12 volts.


I also cut the blue wire and connected it to a longer wire that goes to the SWI-X unit, so that it could receive signals from the steering wheel controls. It gets a little confusing because the SWI-X uses a green wire to receive steering wheel controls, whereas the green wire coming from the steering wheel is actually the power wire.


Also required was a separate power wire going to the SWI-X so that it can operate. I mounted the unit inside the CD holder console (see below). I like this setup because it allows easy access in case I need to re-program the unit. I drilled two holes in the plastic CD tray insert (easily removable with just two Phillips head screws), a bigger one for the group of wires on the right side of the unit, and a smaller hole for the IR emitter wire coming out of the left side of the unit. I ran the wires straight down the center of the console and up through the back of the dash. Under the plastic insert seen below is a perfect place to hook up the ground wire. There's a couple of nuts on studs that secure part of the center console. Excellent grounding.




Development



Development



Look closely and you'll see where I mounted the IR emitter. It needs an unobstructed line of sight to the IR receiver on the head unit. The Sony unit receives its signals on the right side of the face, so I mounted the IR emitter on the right side of the center console.


The best part about the SWI-X is that you can make each steering wheel control do anything you want (within the limits of the head unit's remote control). If you want the volume controls on the steering wheel to scan for radio stations, make it so. Overall, a nice little gadget.



Copyright 2025