Big Stereo upgrade for '08 GXP

**masonv6** · 08-24-2014

Hi, I just recently bought my '08 grand prix gxp. I was wondering if there is anything I should know before I start to do the install (or odering). My factory stereo has the Monsoon system with Navigation. I will be installing (2) 1200wrms 12" subs, with a 2200wrms amp. I will be putting in component speakers in the front doors and into the 6x9 cutout in the rear deck. These speakers will be ran by a 125w x 4 multi channel amp. I will be installing a 240amp HO alternator. The exact HEAD UNIT I havent decided on yet. I will be keeping steering wheel controls as well.
One of my questions is, Do I have to buy the AXXES GMOS-01 for the car if I do not plan on keeping ONSTAR, or can I buy the regular wiring harness.
If there is anything unusual with this car that someone should know before they upgrade a stereo like what I am doing I would really like to know anything I should watch for or be aware of.
Has anyone done a flush mount with components in the front doors? If so how you did it exactly would be nice to know as well
Thanks you for your time

**industrialfish** · 08-24-2014

To do it right, you actually need the GMOS-04. Without it you won't be able to power the radio because we don't have a switched 12V at the harness, you won't have door chimes, and the radio won't stay on after you turn the key off.

EDIT: Wait a sec. If you are not using ANY of the factory equipment at all, wiring harness won't matter at all, just run a switched power from the fuse box.

**masonv6** · 08-24-2014

http://www.grandprixforums.net/threa...Stereo-upgrade

I just found this thread. What does he mean by building off the monsoon system for his HUD to work correctly. Is there alot more than meets the eyes with these cars stereos

Taking the factory stereo out won't F-UP my HUD will it?

**industrialfish** · 08-24-2014

No, you can eliminate the entire system and the only thing it will do to the HUD is lose your turn-by-turn, radio info etc. He's talking about keeping stock head unit and building off of that so that he keeps the HUD nav.

**simbah** · 08-25-2014

If you choose to keep the warning chimes for your car and opt to remove the Monsoon amp then the GMOS-01 harness is the one you want.If you don't care about chimes then, yes, an ordinary harness will work but you will have to run a 12v power from your fuse block for ignition power.

**CrazyGuy03** · 08-25-2014

Question. Where are you getting your alternator from?

**masonv6** · 08-29-2014

I plan on either a mechman or singer ho alt.

**tc300** · 08-29-2014

singer!! all the way

**tc300** · 08-29-2014

start with a good head unit.. your system will only sound as good as the signal it starts with....

**masonv6** · 09-24-2014

where in the fuse box to I add the 12v switch or how exactly.

**2dee11** · 09-25-2014

I also just bought an 08 GXP and plan on a big audio upgrade soon too. Excited to see what you do.

in my 05 I used the regular harness lost on start (ehh) lost date in dic (ehh) lost chimes (loved!!) but I just ran an add a fuse in what I think was the sunroof fuse and ran the wire to the red power wire on the HU

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