double0alero
New member
I figured there's been a few questions on this, so I'll just post up a little deal on the different type harnesses and so forth that are available for the alero.
Aftermarket Headunits, Wiring Harnesses and Class II
This page focuses primarily upon problems that arise from installing an aftermarket headunit into a vehicle that has GM's Class II databus. As an Alero owner, this is Alero/Grand Am specific. While the basic information and concepts will apply to any car the employs the Class II system, part numbers and such are specific to the n-body platform.
When I was attempting to find information regarding wiring harnesses to use in my 2001 Oldsmobile Alero, I was able to find plenty of information. Too much information, almost. Spread out in many places. Sometimes people saying the same thing, sometimes saying different things. On some forums, people with would say that they just used a simple harness and didn't lose chimes! The only problem with that is that they didn't say they have a '99. The 99's don't have the Class II system...they wouldn't have lost them anyway. So someone might read that and then think that they don't need a relocation harness or a replacement interface when, in fact, they do. This is my attempt to bring as much information as possible into one place, as accurately as I can manage.
This page is divided into six sections:
Class II or not?
GM's Class II data bus connects several electronic components throughout the car. The radio is one of these devices. The Class II system routes the warning chimes (headlights on, low fuel, etc.) through the radio. The radio receives a signal and then sounds the chime through the left front speaker. To check to see if you have a Class II system, listen for your chimes. If they come from the left front speaker, you've got it. If they come from the middle of the dash or somewhere other than the left front speaker, then you do NOT have the Class II system.
What is Retained Accessory Power (RAP)?
Retained accessory power is a feature on most (if not all) recent GM vehicles. While I'm not sure when RAP was included in specific vehicles, it was not introduced on all models simultaneously. RAP provides power to accessories in the car (most notably the radio) after the ignition is turned off. It will stay on for about 10 minutes or until the driver's side door is opened. You probably already know if your car has RAP. If you don't, the next time you get out of the car, turn the car off . If the radio stays on until you open the door, you've got it. To the best of my knowledge, RAP is controlled (at least partially) by the stock headunit. In my own testing, I determined that none of the wires going to or from the headunit carry any voltage to indicate whether or not RAP is active. The radio receives a signal from the body control module telling when to turn on and off. This explanation would also account for the CD player powering up when you open a door or use the key fob (allowing you to remove a CD without turning the car on...and also allowing the radio to send voltage down the remote turn-on wire for the factory amp). It may be that if the stock headunit is removed from the databus that RAP doesn't work correctly because the databus has been interrupted. This may be an incorrect assumption, but I am unaware of a GM car the has RAP that does NOT have the Class II radio. So if you have RAP, check that left front speaker to confirm where the chimes are coming from.
Now that you know whether or not you have a Class II system, you can decide what to do.
If you do NOT have a Class II system, I consider you lucky. Go buy a cheap wire harness and treat the install like any other car you may have owned in the past.
If you do have the Class II system and you intend to replace it with an aftermarket headunit, there are three basic approaches:
http://peripheralelectronics.com/2002/home.asp
Aftermarket Headunits, Wiring Harnesses and Class II
This page focuses primarily upon problems that arise from installing an aftermarket headunit into a vehicle that has GM's Class II databus. As an Alero owner, this is Alero/Grand Am specific. While the basic information and concepts will apply to any car the employs the Class II system, part numbers and such are specific to the n-body platform.
When I was attempting to find information regarding wiring harnesses to use in my 2001 Oldsmobile Alero, I was able to find plenty of information. Too much information, almost. Spread out in many places. Sometimes people saying the same thing, sometimes saying different things. On some forums, people with would say that they just used a simple harness and didn't lose chimes! The only problem with that is that they didn't say they have a '99. The 99's don't have the Class II system...they wouldn't have lost them anyway. So someone might read that and then think that they don't need a relocation harness or a replacement interface when, in fact, they do. This is my attempt to bring as much information as possible into one place, as accurately as I can manage.
This page is divided into six sections:
- Basic Class II info, RAP and Harness Options will help you determine whether or not your vehicle has a Class II system by determining where the warning chimes come from and whether or not you have the retained accessory power (RAP) feature. Based on those two things, you can then see the pros and cons of "the three R's" when you replace the stock headunit: removal, relocation, or replacement interface.
- Basic Wiring Harness/Antenna Adapters/Dash Kits gives suggestions (including part numbers and prices) for the harness you'll need if you intend to simply remove your stock headunit, along with the two other necessities, an antenna adapter (the stock antenna plug is much smaller than the aftermarket plugs) and a dash kit in which to mount your aftermarket headunit.
- Relocation Harnesses provides part numbers and commentary about the two most popular relocation harnesses.
- Replacement Interfaces provides part numbers and commentary about the five Class II radio replacement interfaces currently on the market.
- Factory Monsoon Audio Systems addresses a few of the common questions about the Monsoon system, including amp location and the mismatched impedance 6x9 coaxial speakers.
- Sources provides many links to places that I culled this information from. Car owner forums, manufacturer's sites, retailers, etc.
- Type of car (Grand Am, Alero, etc.)
- Model year
- Type of sound system (Monsoon, "premium", standard, "Sun & Sound" package, etc.) and whether or not you have (or had) the factory-installed amp in the trunk
- Do you have the Class II system?...Does your car have retained accessory power (RAP)?
- Which harness you used (and comments as to how it worked)
- Features that you may have lost (chimes, RAP)
Class II or not?
GM's Class II data bus connects several electronic components throughout the car. The radio is one of these devices. The Class II system routes the warning chimes (headlights on, low fuel, etc.) through the radio. The radio receives a signal and then sounds the chime through the left front speaker. To check to see if you have a Class II system, listen for your chimes. If they come from the left front speaker, you've got it. If they come from the middle of the dash or somewhere other than the left front speaker, then you do NOT have the Class II system.
What is Retained Accessory Power (RAP)?
Retained accessory power is a feature on most (if not all) recent GM vehicles. While I'm not sure when RAP was included in specific vehicles, it was not introduced on all models simultaneously. RAP provides power to accessories in the car (most notably the radio) after the ignition is turned off. It will stay on for about 10 minutes or until the driver's side door is opened. You probably already know if your car has RAP. If you don't, the next time you get out of the car, turn the car off . If the radio stays on until you open the door, you've got it. To the best of my knowledge, RAP is controlled (at least partially) by the stock headunit. In my own testing, I determined that none of the wires going to or from the headunit carry any voltage to indicate whether or not RAP is active. The radio receives a signal from the body control module telling when to turn on and off. This explanation would also account for the CD player powering up when you open a door or use the key fob (allowing you to remove a CD without turning the car on...and also allowing the radio to send voltage down the remote turn-on wire for the factory amp). It may be that if the stock headunit is removed from the databus that RAP doesn't work correctly because the databus has been interrupted. This may be an incorrect assumption, but I am unaware of a GM car the has RAP that does NOT have the Class II radio. So if you have RAP, check that left front speaker to confirm where the chimes are coming from.
Now that you know whether or not you have a Class II system, you can decide what to do.
If you do NOT have a Class II system, I consider you lucky. Go buy a cheap wire harness and treat the install like any other car you may have owned in the past.
If you do have the Class II system and you intend to replace it with an aftermarket headunit, there are three basic approaches:
- Remove the stock headunit. Buy an inexpensive wire harness to match up to the factory harness and then connect your aftermarket harness. You WILL lose all chimes...this may not be a bad thing to some people. You will also lose RAP. Since there is no switched accessory lead in the factory harness, your aftermarket headunit will still need a one. Most people will tap a fuse in the driver's side fuse block (often the windshield wiper fuse) and run that wire through the dash and connect it to the red wire on the aftermarket harness. Now your radio will be on if the ignition is at "ACC" or "ON" but will go off immediately when you switch to "OFF". No retained accessory power.
Pros: Least expensive, easy, no chimes (depending on your point of view...)
Cons: No chimes, no RAP, must tap fuse and run wire through dash
- Relocate the stock headunit. Get a relocation harness and move the stock headunit to the trunk (some people have also put it under a seat). The relocation harness will plug into the factory harness in the dash and provide wires for the harness from your aftermarket radio to connect to. Long wires will also lead from the factory harness...long enough to reach the trunk, where you can put the stock headunit. Most kits will include a separate speaker. Connect the proper wires from the relocation harness to that speaker and then mount the speaker somewhere behind the center console. Since the radio is still on the databus, it will pick up the signal to sound the chimes when appropriate and route the signal through the small separate speaker. The aftermarket headunit still needs an accessory switched lead as described above, therefore no retained accessory power.
Pros: Keep chimes
Cons: More expensive, no RAP, must tap fuse and run wire through dash
- Replace the stock headunit with a Class II module. Until recently, this option was not available. The Class II module plugs into the factory harness and provides wires to connect to the aftermarket harness. The module listens to the databus for the chime signals. When it finds them, it either plays the chimes on an internal speaker or it sends a signal to a small separate speaker that you mount behind the center console. The main difference is that the module also listens for the signal to tell the radio to turn on and off with RAP. It then provides a 12 volt lead to connect to the accessory switched lead on the aftermarket harness.
Pros: Keep chimes, keep RAP, no relocating the stock radio
Cons: Most expensive
http://peripheralelectronics.com/2002/home.asp