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Old 09-11-2006, 07:43 PM   #1
TheKomoman
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Default C6 How to Bypass the PAC AOEM-GM24

Quite a few of us have used the PAC AOEM-GM24 modules to get pre-amp output from the stock head units while maintaining the wiring harness. Since we did my installation I have been chasing after *something* in my system that just didn't seem right. I have a JL Cleansweep in front of the amp to flatten the signal as analysis friends & I did showed a non-defeatable bass roll-off as gain increases coming from the NAV head. It has been suggested to me that the PAC module may be the culprit and that was among the reasons I pursued this modification. Steve Germany also refers to it as "the noise inducing black box" so now I had a few reasons to do this.

What I essentially did is make the PAC into a breakout cable. I cut the wires leading into the modular connectors on each side of the box labeled OEM-1. Then I used a "european style" terminal strip to link the wires.

Click the image to open in full size.

I went left-to-right, front-to-back across the strip. The PAC wire colors are white for left front, gray for right front, green for left rear, purple for right rear. The + is solid, the - has a black stripe.

After plugging everything back in and verifying signals in the proper channels I just put so electrical tape over the exposed wires from the - on the female RCA's and tucked it in where the PAC module had been.

Click the image to open in full size.

After buttoning everything back up I re-ran the calibration on the Cleansweep at the same gain output from the head so that everything was equal. Then played the same couple of CD's I had listed to before doing this so I had a solid basis for comparison.

The difference was rather dramatic. Whatever that OEM-1 box was doing, whatever it's claim about being able to increase gain, well the output from the head was MUCH higher without it, which keeps the amp from having to work harder and gets a chance to really shine. It was like a veil had been lifted from my system. The highs and midbass woke up and FINALLY I was hearing what I had hoped to hear when I planned out this sytem.

It's a bit annoying that I now essentially have a $50 wire harness, but it does get the job done. YMMV of course, but it was well worth opening my console YET AGAIN as far as I'm concerned!
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Old 09-11-2006, 09:27 PM   #2
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Ya know, I purchased a PAC AOEM-GM24 when I installed the aftermarket system in my C6 with the Blose system and XM. I was trying to keep the Delco 6 disc in-dash CD changer (and the XM) while I waited to get my Pioneer AVIC D2.

Well, the PAC AOEM-GM24 was absolute and complete garbage! I had no midbass, and ZERO bass. Even the tweets sounded dirty. I immediately ripped that POS out of there. It sucks sinking 50 bucks into something I won't even be using, but hey, that crap had to go. Had I seen this writeup a few weeks ago it might have prevented several swear words from echoing throughout my neighborhood.

I wonder if I can chop it up and use parts of it for the AVIC D2 install this weekend? Hmmmm....

BTW great writeup Dan TheKomoman!
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Old 09-12-2006, 12:31 AM   #3
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Nomad,

Yes, you can. I wrote this up over a year ago but TheKomoman did a MUCH better job than I did.

Two thumbs up for the great job and pics that TheKomoman did!

Too bad that someone does not do the PAC OEM GM-24 black box cut out mod and offer it up for sale to the board!

This is now in the Corvette General, C6 Audio FAQ

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Old 09-19-2006, 11:16 PM   #4
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Another way to do this for less $$ is to buy one of the wire only cell mute adapters ($20 to $30) which essentially gets you a 12- and 24- pin set of extenders that you can do the surgery on for tapping the 4-channel Low Level output from the 24-pin harness without buying the box part. Just use the 24-pin part with the taps cut off and insert it in series with the radio. True plug and play.

According to the Shop Manuals the 8 wires under discussion are twisted by channel as well as recieving a bare wire and wrapped shield drain that is connected to either the Bose Amp (U65) or non-Bose amp (U65) but not the HU. This implies some interference concerns that GM felt worth adding that to for the short run btween the HU and amp in the RHS footwell.

Anybody noticed any noise increases by running the wires unshielded?

FWIW that simple cell harness is by Cellsite and the model number is GMCSS-2. Its out there from a number of sources online. I used this in a 2003 Denali with a Parrot 3200 (that I replaced with the C6) and it was really nice (Denali had OnStar) for calls in the car. I was going to re-use it (finally having shop manuals allowed me to verify the pinouts for the cell phone part in the C6 which are the same as the 2003 Denali) for the upcoming audio upgrades until I found the following whch may be of interest.

There is a Peripheral Electronics product (PXGM24HF) that has the same function, adding a cell hands free kit, but this time with a box. It still has the same wire extension that could be cut for plug and play HU outputs. The difference here is that the mono signal from the hand-free has a simple line amp and its level is adjustable allowing it to be matched to the OnStar system. More importantly it has a true RAP output wire that cranks out 12V at 500mA while the RAP and normal operations are present.

This means that you could pop a relay with that and finally get a true RAP circuit for all the powered stuff that you wanted to switch like the rest of the car - no more heated seat tapping and so on. The setup I'm planning has amp upgrade, better speakers, cell hands free as well as an iPod integration so that product is just what I need. I will be recieving that Friday and am planning a raw hookup of the mods this weekend for testing - I'll post back what I discover...
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Old 09-20-2006, 07:32 AM   #5
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Great info alusk, thanks very much!!!

I exchanged a couple of e-mails with PAC last week and the sales guy told me they have a part number ADD-GM24 that is the 24 cable harness with the 8 wire line level output breakout. It would sell for around $15-$20.. that is if I could find anybody that sells it! I already dropped my $50 with the AOEM-GM24 so I have the harness but I was hoping to find a source of a cheaper cable to recommend. That Cellsite cable sounds like it may be the ticket, plus add in the hands free option. I really like that idea.

Can't wait to see what you find out!
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Old 09-20-2006, 04:52 PM   #6
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I am looking foward to your findings as well! Be sure to post!
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Old 09-20-2006, 08:45 PM   #7
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I just took my AOEM-GM24 out of the package,and the front harness that plugs into the black module is labeled ADD-GM24.Is that the way your's were labeled as well?
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Old 09-20-2006, 09:01 PM   #8
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FWIW I'm guessing that the box part is generic and that the ADD-GM24 part is one in series of harnesses they sell to allow the box to be used across the differing manufacturers whose HU's spit out some sort of low level audio signal.

Unfortunately that may mean that the usual resellers wont have it. To get that you may have to go to PAC like your buying a spare part direct from them and go that route...
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Old 09-20-2006, 09:18 PM   #9
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you are correct on how it works, its just a harness that basically plugs into a universal box
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Old 09-20-2006, 09:18 PM   #10
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Quote:
Originally Posted by pentavolvo
you are correct on how it works, its just a harness that basically plugs into a universal box


And I think alusk is correct as well.. finding the ADD-GM24 as a separate item may be impossible.
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Old 09-20-2006, 09:36 PM   #11
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Why not buy a standard gm harness and the matching reverse harness and basically splice together what needs to stay togehter and tap into what you did.

I did this on my gf's subaru a few years ago to avoid hacking the harness
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Old 09-20-2006, 09:41 PM   #12
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Quote:
Originally Posted by pentavolvo
Why not buy a standard gm harness and the matching reverse harness and basically splice together what needs to stay togehter and tap into what you did.

I did this on my gf's subaru a few years ago to avoid hacking the harness
The GM harness would be easy to get.. but the reverse harness that plugs into the head?
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Old 09-20-2006, 10:15 PM   #13
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get me the model number of the std gm harness that the vette uses and ill find u the reverse it should be readily available i forgot what harness the c6 uses off hand though
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Old 09-20-2006, 10:17 PM   #14
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could this be the piece u guys are looking for http://www.discountave.net/adpacmoauine.html
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Old 09-21-2006, 07:30 AM   #15
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Quote:
Originally Posted by pentavolvo
could this be the piece u guys are looking for http://www.discountave.net/adpacmoauine.html
Thanks, that exactly the one we've been looking for!
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Old 09-23-2006, 06:21 PM   #16
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Default No Go on using the GMCSS-2 or PXGM24HF

I had a chance to try both of those harnesses today and unfortunately had little success. Both of them would not switch the Nav HU from whatever it was playing to the Parrot unit for cell phone operations.

As near as I can tell its the initiation of the cell session - the only way I could get the HU to mute and then look for low level mono input signal was to press the OnStar phone button on the rearview mirror. This implies that the the command to switch is being handled by the serial data line to the radio.

I then took the PXGM24HF unit and removed its Serial Data line segment from the 12-pin harness (came that way) and tapped it onto pin A1 in the 24-pin harness at the radio to get at the data signal - hopefully this would have had the black box act like the OnStar button when triggered by the Parrot unit and cut out the OnStar but it didnt work at all.

One small victory however is that the RAP feature of the PXGM24HF worked perfectly. When it was tapped to the serial data line the RAP LED went like the rest of the car when opening the door or forcing the RAP on and off with the starter button so I suppose you could use it just for that. That gives me enough faith to try their other RAP product.

That is the GMRAP that they state works for all GM through 2005 - its about 50 bucks so I may try that and see if it works with the 2007 as it provides 12A of power (versus 500 mA for the PXGM24HF) so I can use it to provide power to the Parrot and H-K iPod controllers which require switched power. It is a snap to set up with 4 wires. I'll get that ASAP and report my findings.

As for the Parrot install I'm down to doing it post-HU and inserting 1-channel cell signal into the low-level outputs with low power non-latched relays. At least there is an active trigger in the Parrot unit to switch so I'll get and make calls alright but will lose any HU output when doing so. I'll have to build a swither box and will be doing that ASAP - as before if I can get it to work I'll report my findings.

If anybody has put in a handsfree solution with the Nav HU and OnStar any other way I would appreciate you experiences.
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Old 09-24-2006, 12:53 PM   #17
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Here's my latest and hopefully FINAL version of the harness. We took some quick disconnects and crimped the males on the harness side, females on the RCA. Clip 'em together, a little electrical tape to secure and insulate, done!

Click the image to open in full size.
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Old 09-25-2006, 10:10 PM   #18
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So, did you do away with the European Terminal Strip in the first post? Where did you get the RCA females and the quick disconnects? Can you pick those up at Radio Shack or something?

You've gone through several versions....can you briefly list in what order and do you think the sound is getting better each time? Seems like you're just simplifying. Removing the JL Cleensweep, then the PAC unit, now down to a harness and spliced wires.

I just can't bear the thought of taking off the dash again.
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Old 09-25-2006, 10:38 PM   #19
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basically hes down to a harness and rcas, which is all u need. All that is available at radio shack. You could skip the harness if u wanted and splice rca's into stock harness
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Old 09-25-2006, 10:47 PM   #20
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Quote:
Originally Posted by pentavolvo
basically hes down to a harness and rcas, which is all u need. All that is available at radio shack. You could skip the harness if u wanted and splice rca's into stock harness


First I got rid of the PAC. MAJOR difference and I posted the RTA charts in that other thread that shows why. Craig I know you dread the console, but having done it FIVE times now it gets easier every time. A 90 deg pick tool, while dangerous to your fingers, is very handy for getting that power plug clip off. You're selling your system short with that OEM-1 box in the mix, believe me I'm sorry to say.

The Cleansweep became redundant once I had the PAC removed, turned out all it was doing was cleaning up the PAC.

Got rid of the euro harness. My buddy couldn't stand the site of it so he made those female harnesses and made me open the console one more time. As Penta said, those parts are readily available at Radio Shack. Opening the console was necessary anyway, as we had buried the trigger wire in there and we needed to hook it up after removing the Cleansweep.
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Old 09-25-2006, 10:47 PM
 
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