Speakers dead - even after replacing speakers and headunit


Original poster
Apr 4, 2012
06 Trailblazer LS - had the most basic single-disc headunit (no Bose, no amp) and in the past couple of years we've noticed that the sound started crapping out and eventually would only come out of the right front speaker. It'd cut in and out periodically, too - and the sound got so bad over time that it'd simply be a very tinny, weak sound out of that right front speaker.

The TB wasn't getting driven much, so we didn't worry about it - but now my eldest is turning 16 and she needs a car. And, well, she'd like some music.

Replaced the head unit with a cheap single-DIN using the Metra harness, and we got little improvement. We did start to hear sound out of the left front, occasionally - but again it'd continue to cut out and we'd have no sound for a while. So I bought some cheap Kenwood 6.5" speakers for the front doors, and replaced those - used the pigtails supplied with the speakers and crimped them with butt terminals into the red and black wires I'd snipped off the old factory speakers. Still nothing.

Other than a short somewhere between the head unit and the speakers, I'm at a loss.

Any suggestions on a troubleshooting path from here?


Lifetime VIP Donor
Supporting Donor
Jul 22, 2015
Understand that we're probably as much in the dark as you are, right now, until you get some more info. But here's what I'd do first...

Bypass the vehicle entirely with your new HU and speakers.
Connect the speakers to the HU, and find the following leads (refer to the HU instructions, if needed)...
+12v constant (orange, maybe red)
+12v switched (red, maybe orange)
12v ground (usually black)
Any other needed positive voltage connections (Accessory is generally 'yellow', but you probably won't need it for this test). Don't connect the remote turn on lead (generally white / blue stripe). That's for an external amplifier, and we're not introducing that variable here.

If needed, tape off any unused connections, so that they don't stray into the path of +12 power and blow the radio fuse.

Set the volume to minimum (zero).

Hook up those leads to a 12v source (like a car battery, but not the one in the TB, while it's installed in the TB (e.g.; you can remove the battery leads from the TB, and then temporarily hook up the HU to the battery). The HU should be fused, so you'll be able to run this test for a minute or two.

Set your fader / balance controls appropriately. If you only have two speakers, then set the fader / balance to the connected wires only, test those channels, then cut the power and swap the wires accordingly; then repeat the steps.

By doing this, you'll verify that your HU and speaks are working. You can also do this to the old HU (not the factory one), and make sure that it's good, too.

If the HU (one or both) and the speakers are working, then your issue is with the vehicle wiring.
At that point, you'll need to get your hands on a multimeter, in order to test.
But to start, let's make sure to validate your equipment is good, outside of the vehicle.

PS: Don't leave the radio connected to the battery longer than needed to test, even though the radio is fused.

Next things to check, before you get into vehicle wiring... all of the fuse locations related to audio.
Also, download a copy of the wiring diagrams from our site (Mooseman has links in his .sig at the end of all of his posts). You'll want to have those handy to refer to, once you're ready to proceed.

Is everything else on the TB working, electrically? The reason I ask... there are several places on the vehicle that provide grounds for multiple components. If other thing(s) are also inop (either 100% of the time or intermittently), knowing what those things are help isolate where to look, first.

Hope that helps. BTW, I'm not as active as some of the other members of the site, so don't be surprised if someone else picks up from here, besides myself, once you report back.


Original poster
Apr 4, 2012
Wow, thanks - this is quite helpful.

A brief morning update - it works! Sometimes!

Speakers were dead again on startup, but after shutting everything down and opening the driver's door, both front speakers started playing.

Upon startup, dead again - but I shut it down while in line for coffee, opened the door, and it started playing - and playing well - from both front speakers. I've abandoned hope for the rears for now until I sort this out.

So I'm thinking there may be some funky grounds. I'll go look for Mooseman wiring diagrams.

Many, many thanks.


Supporting Donor
Dec 3, 2011
Brighton, CO
Can you post your VIN please?

To me it sounds as if it has a amp that is dieing.

Some of the LS models did get higher end radios, depending on how it was ordered.
I can verify with a VIN.
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