I have read a lot of thread about installing aftermarket HU's and am confused. If I buy the appropriate wiring harness, shouldn't i just be able to match up the colors and plug it in? Specifically the red (acc) wire. Why do some people tap into their wiper/sunroof fuse with that wire? Shouldn't i just be able to connect the red radio wire to the red wire on the wiring harness, which would enable the deck to turn on/off with the key?

 

because you need a switched wire so the radio knows when to turn on and off. The sunroof fuse is a switched source that is only on when the key is on or in acc.

 

so i need to ignore the red wire from the PAC harness and run a long wire from the tapped fuse to the red wire coming out of the HU?

 

Depends, if you have an interface that is designed for the RAP feature, then you don't have to run your own accessory wire.

 

correct... Gm cars use whats known as GM lan to oporate the radio. So it turns on and off with Data not voltage. In 05-06 vehicles they do make interface harnesses but its stupid to use them because it just makes a second chime you dont need and cost more. Also the main disadvantage with an interface harness is them breaking. They are in no way shape or form factory spec and you will see on here time and time again people having issues with them broken out of the box or breaking after time. So no real advantage for 05-06 cars. On 07+ they have the chimes going thru the radio so at the very least you get something for your hundred bucks.

If i remember correctly on the cheap harnesses the red wire is connected to the gm lan wire so i would strongly recommend not tapping that and trying to use it for turning on your radio. If you have a module intercafe then your fine it interprets the data and gives acc voltage on the red wire