Monte Carlo stereo situation

Ok so I am going to buy a new car.  Most likely I am going to get a Monte Carlo, new body style.  However, I have been reading that if you change the radio with a aftermarket HU there are some problems, like the OnStar will not work, the oil sensor, door chime, and other problems.  I will probabally get the N2 touchscreen with a new amp and new interior speakers.  What I am wondering is is there a way I can keep all those things (OnStar, oil sensor, door chime) and not have to keep the factory deck in the car, trunk etc.....  Is there a bypass chip or wire or something I can do this with? Thanks!

You need the PAC OS2 interface for the Onstar system to start. Next you need the radio deletion kit for these vehicles as well. It is made by numberous companies, I recommend the Scosche DCGM09 for this. Top Secret, I can tell you but then my wife will kill me.

What is a radio deletion kit?

It is a harness / module that is designed to mirror the functions of the vehicle that are built into the factory head unit. Unplug the head unit and you lose these functions. The new harness allows removal of the factory head unit while retaining the functions that it once controlled. It is a expensive little bugger, but it is 100% necessary.Top Secret, I can tell you but then my wife will kill me.

And if I get the Scosche DCGM09 it will allow me to keep ALL settings from the factory, like alarm, onstar, oil sensor?

No the alarm is not going to affect the deck. And you Need BOTH pieces that forrbidden listed above to keep all functions. GM made it expensive to upgrade these cars.double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

Well, here is the new situation.  I am going to have a aftermarket alarm put on, a viper or python professionally installed, and I am NOT going to keep the OnStar.  So what exact wiring harness would I need for this.  If someone can post a link, it owuld be really helpful. Thanks to everyone who has helpes thus far!

You still need the Radio deletion kit from companies like metra or peripheral. Call any local shop and they will give you an exact price. I know that around here they run for 149.99 Canadian.double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

Cant I use the Scosche DCGM09 that forbidden mentioned above?