factory keyless interfacing

to add remote start you will need to properly hook up to the passlock II anti theft in vehicle ignition and the door lock would be a negative pulse off remote starter or alarm module.
to turn on dome you will need to send proper voltage to dome wire based on what it requires to make light illuminate. Headlights are not usually a standard hook up feature but you could wire them to turn on with dome supervision through a relay.
The trunk release is also a negative that could run off the remote starter module. When you install an add on, it will be an independent system of that that exists in the car already.
Some systems have door lock upon ignition and unlock when key is off, however your vehicle already does this so that won't be a feature you will need.
There is always a way to wire something but figuring the correct way is sometimes confusing. If you have never done work like this before I would strongly advise you seek some assistance, especially with a vehicle that anti theft like yours does.

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The wire I'm test'n isn't doin' what it's supposed to be doin'... I am so glad I printed that tech sheet, with the wrong info.
Do it right the first time... or I might have to fix it for ya

Hopefully I can answer some of your questions/concerns.

The factory speed-sensitive doorlocks won't go away when you install a remote starter.

Regardless of what you install (aftermarket remotes or using the factory ones), you wouldn't be removing any of the factory equipment.

You can add a remote starter, or an alarm, or both, to your factory remotes, but you'll be limited to the range of the factory system.

From your house, see if the factory remote works. If it doesn't, you won't be able to use the remote start from home either.

Even if it does work from your home, keep in mind that it's not going to work from the mall, supermarket, work, friend's condo complex, etcetera.

Besides all that, to put in a new system with aftermarket remotes wouldn't cost much more anyway, and might be easier.

I install Audiovox product, so I'll use their part numbers to give you some ideas.

AS-9076 add remote start to factory remotes

PRO-9233 add alarm to factory remotes

(you could install a 9076 and a 9233 in the same car, but it's fairly complex to install two products in the same vehicle. Only recommended for the advanced installer.)

PRO-9276A or APS-687 Remote start, keyless, trunk, panic, with two remotes and much greater range than factory.

PRO-9776A or APS-787 Same as above, but adds alarm. (combination alarm and remote start)

PRO-9801, PRO-9801XR, APS-997 Same as the alarm/start combo above, but adds greater range, and a 2-way remote with an LCD screen, so you if the car remote started without having to look at it.

AS-GM4 interfaces with your car's PASSLock II anti-theft system for remote start. You'd use this no matter which of the above remote starters you chose.

GM-DLBP from www.bypasskit.com Slightly more expensive than the AS-GM4, but it makes the installation MUCH easier. Interfaces with the PASSLock II, but also helps you with locks/trunk/domelight turnon.

If you're thinking of doing the install yourself, go to www.audiovox.com, click on Customer Service, click on Manuals, and type in any of the above part numbers (but without the hyphens). There, you can read the (poorly written) installation manual, and see what you think.