Car Stereos: 05 grand prix, stock radio, gm vehicles

Question
I have an 05 grand prix and I went to put a deck in it and all these technicians are telling me that they have to put a weird wiring harness in it and run a wire to my stock radio which would be just sitting in my trunk. They say this because the display with the date n time runs off the stock radio. They're also saying my onstar may not work.That would cost me about 60 bucks for the part and 100 if I want it installed by them. I went to try to buy a "connector" from meijer because you can buy most of them for like 10 bucks there... and could only find up to an '04 grand prix. I'm confused! Just wondering if these people are just trying to get money or if they know what they're talking about!

Answer
Hi Alexa,

Unfortunately, they're telling you the truth.

All recent GM vehicles (especially ONstar equipped ones), have all sorts of extra information that goes through the car stereo.  This includes your door chime, seatbelt warnings, onstar data, etc.  As a result, replacing the factory deck requires extra hardware that can perform that part of the functionality that your factory deck does since an aftermarket deck would know nothing about it.

Just buying a harness and installing it will work, but you will lose lots of functionality from your car (including onstar).

Justin