I have noticed a lot of confusion on what wire harness to use on on 04 GP and GTP's to install aftermarket stereos in these cars, so I thought it would be nice to post all the info I know in one post to help anybody out. If anyone has more info to add or see's something incorrect please let me know. There are a few things to consider when you want to swap out that factory deck for something new. First thing is determining what factory system you have. Second do you care about onstar ar door chimes working. Also if you want to use steering wheel controls you will have to buy a seperate interface.


Standard GM harness: This is definitly the least expensive but you can't use the monsoon amp if you have monsoon system. Also you will lose onstar if equipped and door chimes, and RAP(radio stays on until door is opened). You will also have to run a power wire to the ignition switch or fuse box. This harness usually runs $10.


GMOS-01: You will want to run this harness if you don't have a monsoon amp or if you are going to bypass it. This is the harness that I currently have in my 04 Comp G. This will retain Onstar,door chimes, and RAP. This harness runs $100 but if you buy it through Crutchfield with a new radio they will sell it to you fo$50


GMOS-04: This is the harness that you will need to run if you are just replacing the head unit on a monsoon system and want to keep using the factory amp. It had RCA's on it that plug into the aftermarket head unit fot the amp. This will also retain Onstar,door chimes and rap. Same price as the GMOS-01

The GMCO also works with the Monsoon system for sure.. I believe with this one you lose Onstar, but retain RAP and door chimes.

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Thanks for the info

standard harness for me all day if you know what you are doing and you will not lose rap and you can use your monsoon amp.
You can use the monsoon amp or bypass it.
p.s. i hate door chime.