headlights seem to work with the key in this car. doesnt matter what the setting for head lights is, all lights are on at all times unless the car is off.

 

I've never seen a $40 module, and considering I've had many $100+ modules fail over time, I wouldnt trust it. Yuli, I don't remember ever having to run the wire to the fuse panel on a Blazer. Sunfires, Cavi's, Montana's and various other models need it, but the best way to make sure is by metering, as previously mentioned. If you're not getting 12V+, well, now you know what to do

 

I`ve had a $40 Schoshe module in my 2005 sunfire for over a year now with no issues.

Bypassing is not the way I would go about it but its not my vehicle.

I know the Sunfire didn`t have a 12v switched wire in the harness nor do the 2002 Grand Ams.

 

What advantage does the module provide over "bypassing" it?

 

I wouldn`t say there are really any advantages to using module unless you have a picky customer that has to have everything as it was (And we have all had those customers ) but its like anything the automakers put it there somewhat for a reason, sure it can be bypassed and you nay not notice any negative effects, but its a chance you take and may vary between vehicles and options on said vehicle.

A few things that you may miss out on without the module are:
Seat belt warning chime
Key left in ignition chime
RAP (Retained Accessory Power)
+12V Accessory Power at Radio’s location
Low fuel
Low oil level
I`m sure theres more but all I can think of right now

But I just looked up the 1999 without bose\onstar you just need a regular wiring harness no module required.

 

These plus door chime are the only circuits I have seen in the GM wiring diagrams linked to the HU...

Right. The module will convert the data signal into a "proper" 12V+. Another problem I have with the modules is that they are using a glorified relay to pull power from the 12+ constant powering not only the module, but the deck as well for a switched acc. I personally prefer to have a 12+ for constant and a seperate 12+ for acc, as most decks draw from acc for their operating power, not the constant. The module forces the vehicle to power the module and deck from one 18-20awg wire

Also right. Scosche, Metra, and Bestkits all list only the regular harness. Still, meter the acc to make sure you are getting proper power through 12V+. Having strong power through accessory is much more important than through constant... The constant only retains the unit's memory.

Unless you need to interface with a factory amp or need OnStar in a GM, I can't see a use for modules. Door/seatbelt/headlight/whatever chimes are the audio form of idiot lights.