: 2004 Deville strange symptoms after aftermarket Pioneer head unit install w/ harnes

06-17-09, 02:11 PM

I have a 2004 Deville with what I think is the "standard" sound system. No navigation, no bose. It has a sub in the back, 1 speaker in each door, and 2 tweeters in the front corners.

I was frustrated with having to use a FM transmitter to use my mp3 player, considering I didn't have an AUX jack and I didn't have a tape deck (to use one of those adapters).

FWIW, the mp3 player is not an iPod. It uses a 1/8" jack.

So I finally bit the bullet and got an aftermarket Pioneer head unit installed that has an AUX jack, as well as support for USB flash drives and even iPods, which I don't have but may get in the future for this.

Anyway, I had a car audio shop install it for me and they bought a harness to hook it up.

I've been having all sorts of issues with it. For example:

1. Sometimes the Pioneer head unit turns off on its own.
2. The levels move from left to right, even front to back, at times.
3. There was a hiss at first but that was resolved by lowering the volume on the harness. Unfortunately, my max volume is much lower now.
4. Once, the door chime kept chiming over and over, even after the door was closed and I was driving around for 15 minutes. Only happened once.
5. The motor TURNED OFF once while I was driving (dash lights were still on though). I parked, took key out, started it up fine and it hasn't happened since. I'm not certain it's related to the installation of the Pioneer - could be a coincidence - but that's never happened before, and it happened a few days after the install. At that time I was using a USB flash drive. I haven't since because I'm worried that will happen again.

I've brought the car back to the shop and the guy doesn't know what the cause of these issues are (the main ones being the unbalance audio levels and the Pioneer powering off).

The way I understand it, the harness lets me use my existing amp(s). It just re-routes the wires so to speak.

I'm here looking for general thoughts from anyone who may have run into similar problems before, or who has a guess as to what the root cause of these issues is.

For example, was it a bad idea of using a harness? Should I instead, run new speaker wires and use a separate amp?

Are the audio/electrical systems in 2004 Devilles finniky to 3rd party "mods" like this?

Have other people seen these sorts of issues?

Could the cause simply be due to a defective Pioneer head unit?

Any other thoughts?

Thanks for your time.

06-23-09, 10:56 AM
Did the shop install the factory headunit in the trunk? If not that could be your problem. The factory headunit needs to stay hooked up for everything to work correctly.

06-23-09, 11:38 AM
No, the factory head unit was removed completely and is in my house now.

What do you mean, in the trunk? Where would it connect? Are you being serious or sarcastic? This sounds very strange.

06-23-09, 03:29 PM
No im serious. You have to leave the factory headunit hooked up and the best location is inside the trunk. Some people tie it down with L-brackets others use velcro. You have to run the wires to the trunk in order to hook up the headunit.

06-23-09, 03:44 PM
From what I've heard, that's the "old school" way to do it, before there were such things as harnesses. I have a harness now that I'm using to connect the aftermarket Pioneer head unit. Considering that, should I still have the factory unit connected, i.e. in the trunk?

06-23-09, 04:11 PM
No ask around here on the forum, everybody that has taken the factory stereo out of the car has experienced weird electrical problems.

06-25-09, 11:07 AM
I did a search for "head unit" the electrical and audio threads and I do see that others have run into strange issues, and that keeping the factory head unit in the mix is needed, but I don't see any details as to exactly how to connect it, especially related to my 2004 Deville. Still, this information suggests to me that the cause of my issues are not due to the harness or head unit being defective. That's not the kind of information I was hoping to see (I was hoping it would be an easier fix by swapping the harness or head unit), but it's still valuable.

It looks like I have two options here for "properly" using this aftermarket Pioneer head unit (for resolving these strange issues):

1. If I want to keep using the harness, which utilizes the factory amp/amps? in the trunk, I need to put the factory head unit in the trunk and somehow "wire it" into the system. Can I get details on this, i.e. exactly what wires need to go where, so I can share this information with the audio guy?

2. Ditch the harness, bypass the factory amp/amps? in the trunk, and run new speaker wires directly from the aftermarket Pioneer head unit to the speakers. The factory head unit would not be needed in this case. Since the Pioneer wants 4 ohm speakers, I would need to make sure that mine are 4 ohm (see my other recent topic) and, if not, replace them with aftermarket 4 ohm speakers.

Is this accurate? The more details the better, so I can explain this to the audio guy. He's kind of being hard headed about this, unfortunately, but that's another story.

Thank you.

06-25-09, 12:16 PM
Ditching the harness and running new speaker wires won't cure your situation. The many computer modules in the car communicate over a serial data bus. The radio itself is one of the computer modules as indicated by the IRC test that is run when checking codes (Integrated Radio Control). When the factory head unit is removed from the bus, the communications are disrupted. I'm not sure how it is done, but the data wires at a minimum are run to the head unit and it is placed in the trunk. One of the members that has done it should be able to elaborate.

06-25-09, 12:43 PM
OK, this is starting to make sense now.

If I can get details about that data wire(s), that would be super. I suppose I just need to know the color(s)? Again, 2004 Deville, no Bose, no Navigation, 2 tweeters in the front corners, 4 door speakers and a sub.

06-25-09, 12:58 PM
The data wires in my 2000 Seville are a light purple color. I take it you don't have a factory shop manual?

06-25-09, 01:18 PM
Sorry, I don't. What brand manual is highly recommended?

I did more digging around and found some helpful, info here that's related to an older Deville:


CadillacSTS2003 also said they are purple so hopefully that's the same in my '04.

He also recommended attaching other wires to the factory HU like ignition and remote. Would you agree with that?

06-25-09, 02:07 PM
The factory manuals from Helm, Inc are the ONLY way to go. The can be had on eBay or from Helm at www.helminc.com. The Haynes & Chiltons manuals are crap for the Cadillacs. Yes, I agree that the ignition and remote wires may be necessary too...however, I don't know for sure. Jason (Cadillac2003STS) is the foremost authority on these systems and if he said they need to be connected, then they probably need to be.

06-26-09, 11:25 AM
Yeah your harness is not the problem at all. Your gonna need your harness to connect your pioneer, you just have to leave the stock headunit hooked up like chaz said. Contact Jason and have him walk you through the process.

06-26-09, 05:31 PM
Well you all got me pointed in the right direction and I definitely appreciate that!

Well Jason's private message mailbox is full hehe.

Considering I don't (yet) have a manual, I think I just need to know what the wire colors are for the wires that I need to connect to the factory HU.

Sounds like purple or light purple for the data wire(s).

Generally, what colors are the remote and ignition wires? It seems like those are the only others I need to worry about.

Other questions:

1. Should the factory HU's ground be connected to the same ground that the harness and Pioneer HU are connected to, or should it go to its own ground, i.e. the chassis somewhere?

2. I'm considering just doing this myself, or with the help of my brother who's more of a "hands-on" guy. About the physical cabling, would it be OK to use a cat5 cable (I would guess shielded twisted pair / STP), to make a clean cable run? Probably a stupid question, but they are better than stupid answers, as they say. This would be for the data, ignition, and remote wires, of course, not for the 12V which would be a separate run.

06-27-09, 08:41 PM
Sorry for the "double post". One more question.

What is the part number for the harness that's recommended for my 2004 Deville (non bose)? I'm using the METRA GMOS-06. Is that the correct one?

06-27-09, 11:30 PM
Well if auxiliary input is what you need, you should have read my posts before going aftermarket. I have solution to AUX input ANY Seville/Eldorado/Deville/Catera ‘96 to ’03.
Just connect the data wires together at a minimum to close the network gap (although the network is designed to work with one missing device per network loop). The data wires are the ones connected to pin E6 and F6 on HU connector (and yes are purple, so do other wires thus don't go by color go by pins). Personally I would go back to OEM.

Here is how the network works (imagine a circle that starts with device A then goes to B then to C then to D and back to A again (each device has two wires can not be called IN and OUT does not works that way). Now imagine removing device B, in that case any of the reaming devices are still connected to the network, is true A is no longer connected to C because B is missing but no biggie since C is still connected to D witch in the end is connected to A. But now remove device D from the network (you might need to use a pen and paper to understand better). Well in this case you just completely insulated device C from the network (nothing connects to C anymore). Your car has about 3-4 of these A-B-C-D…-A loops connected together to a common point witch is your diagnose port.

07-05-09, 04:10 PM
I agree you can do this replace your factory in you trunk, make a harness for you poineer run your constant and ingiton to a fuse rationg that's the same the radio requires and run new speaker wire on the ground find a good piece from the dash boards frame should be good. I've seen these new radios in caddys and the newer the car is bigger the pain. Your cars happy your happy

07-05-09, 05:39 PM
where are you located
sorry for the long absence on my part

02-20-13, 11:45 PM
This is the problem and i GUARANTEE if you listen to me you will solve it. DO NOT GET THE METRA GM0S-06 harness for aftermarket stereos. Get the PERIPHERAL GMAH-32 instead. Anybody saying the METRA harness isnt the problem has not done their homework.

02-24-13, 07:30 AM
The Metra isn't an interface at all. It's a line leveler wired to a GM 32 connector. The data bus lines (E6 and F6) are shorted together.
I will give them some credit though. They picked up the serial data for their steering wheel interface to work. If they had only taken that concept and applied it to the GMOS line to answer SOH messages all would be good.
The PAC takes the voltage drop across the resitors in the Comfort and ent. interface.
Peripheral does not make an interface for the Eldos. Bummer.
If the PAC does not work as expected, I will be hacking one these boxes.

02-26-13, 08:17 AM
Well if auxiliary input is what you need, you should have read my posts before going aftermarket. I have solution to AUX input ANY Seville/Eldorado/Deville/Catera ‘96 to ’03.

Except I believe this Cadi has the same stereo as I do in mine, which there is not yet a direct solution for. 04 Deville Base, no Bose, no tape? http://www.cadillacforums.com/forums/cadillac-audio-video-security-systems/282412-aux-input-base-deville-no-tape.html

03-01-13, 07:01 PM
Listen to N*.
He knows what he's talking about.
There is always a solution.