Add aftermarket HU & AMP but keep Onstar
 

I have an '09 w/o the Pioneer system but WITH OnStar.
I want to keep the OnStar functions.
How does one change to a Pioneer 8100NEX and add 4-channel AMP and keep the OnStar system part of the loop?

Anyone done this before?

ACTUALLY, let me ask this:
I presume, when using the Metra GMOS-LAN-04 Harness, if you connect it to your 5v RCA outputs of the HU, then on the otherside of the GMOS-LAN-04 box, you get 5v outputs of audio, and they are not amplified in any way by the GMOS-LAN-04?
If that's the case then I know what I need to do: Just cut the harness wires and re-terminate them with female RCAs.

That's IF the vehicle-side harness connection for the non-Pioneer system is the same as the non-Pioneer system.

pioneer and non pioneer have the same connections. Only difference is the amp turn on/remote wire and the RCA instead of speaker wire.

THe issue you are going to run into is your amp input. The HU will have the RCA outputs and the GMOS Lan will have the onstar output. You could run the HU through the GMOS as expected to get both together but then you will need to rig some RCA ends on there and hope theres no noise in the process. Or just add another speaker under the dash or something for just onstar.

If you didnt have the onstar requirement i would say get rid of the gmos and go with a cheap harness

Basically, yes, my thinking also is to add RCA connectors at the input and output sides of the GMOS. Input side is already bare wire, so it's not so bad. Output side is pre-terminated to the vehicle-specific harness, so those wires would be cut and re-terminated.

1. What inhereintly about adding RCA connections to the wiring leads your concern for noise?
2. Outside of noise, do you think there will be a negative Sound Quality impact or Pre-Amp voltage drop due to using a GMOS to mix Onstar into the pre-amp audio stream?
3. What "cheap harness" would you use?

Upon consequential thoughts, the dedicated service speaker idea isn't too bad. I could install a center channel make it a later project to build a priority muxer which would take chimes, on-star, and maybe 1 other input straight to a custom center channel. Thanks.

However, I'd still like thoughts on my questions above.

input side should already have RCA connections.

1. RCA low level signal in a car enviroment is very supceptable to noise. Most RCA cord will utilize on of 2 different technoligies to fight that and some will use both. Either way having neither isnt a good idea and should be avoided. The length is short so that is good but its around a bunch of electronics so not the best place for bare wire for signal.
2. possibly. Its hard to tell but your much better off using it as input then the opposite of putting the amp output into the gmos.
3 metra 70-2104... the only advantage of the module harness is you dont have to tap the fuse box and it works with onstar. Since you probably arent going to use it to interface with the speakers and even if you do you are going to be slicing it up it makes it less appealing. Its like an ikea table. good for someone wanting to put the shit together and call it good but if your going to modify it anyway then you might as well just go out and buy wood instead.

3) Not sure that alone is sufficient since I am installing a Navigation unit. Still need to restore chimes and R.A.P. and then I also need VSS, backup, and illumination signals which I believe are all on the CAN bus. I'll reconfirm. GMOS module basically done all of that, including steering wheel controls. The only EXTRA thing it had was the OnStar, and now my new plan (to use external speaker should I actually want to run OnStar), bypasses the downfalls of keeping OnStar for now.

Unless I am missing something I still need some type of module, not just a harness.