I've owned my loaded '84 black Caprice since new. It was a no radio car (which is what I wanted, last year of the awful OEM stereo in B-body) and I've had my Mitsubishi component stereo in it since new.
I found that some 2002-2005 Buick'* had RDS and XM radios that almost look period correct, but they are miserable class 2 serial bus communication units.
Here is the 'original' radio. On it'* last leg, I've repaired it so many time in 32 years and 257K miles in this car. The original pictures aren't the greatest.
Here is the new radio with LED back lighting (missing ***** in this picture);
The whole monstrosity ready to go in the car;
The final fit. The XM antenna is just sitting in the defrost opening at the moment. That is the aux input in the radio surround on the right;
n this particular radio (2005 LeSabre), the actual off and on is controlled by the Dash Integration Module (DIM). It is the Power Mode Master (PMM) in this car. It will not turn on with power applied when the off/on switch is pressed without the DIM connection over the single wire, class 2 serial bus. I assume this is part of idea behind the silly Theftlock scheme. Removing the EEPROM, which was common on many of the class 2 radios to bypass the Theftlock, only results in a radio that will not turn on normally and loses presents in this style (the seek >, preset 5, and power will turn it on for 10 minutes, like all of the class 2 series).
The Instrument Panel Integration Module (IPM), sometimes mistakenly called the Body Control Module in aftermarket literature, is programmed to match the VIN in the radio (or vice versa), other wise, the radio Theftlocks. It is programmed with the GM Tech II scanner via the OBDII connector, which I included in my installation for possible future needs, even though I have a matched system (which only costs me $50). Other than that, the only other function of the IPM in the radio application is to control the dimming of the vacuum fluorescent display. Without the IPM, the display darkens as if the lights are on. The light sensor in the dash of the original car controls the lighting scheme for the entire car. This module does have many of the car body functions in it, but I only included it to keep from implementing my own design to control the brightness of the display internally in the radio. To get away from using the light sensor, I put a 2.2K resistor across the connection of a cheap, Bosch type relay. This makes the IPM tell the radio to brighten the display over the class 2 bus. When the dash lights come on, the relay opens which causes the IPM to darken the display. The normal, button back lighting is controlled by the dash lighting dimmer, though I have replaced all the miserable 3mm bulbs (8 of 14 were burned out in a beautiful car that only had 95K miles). The radio face has 2 voltage regulators that darken 6 of the bulbs (where 5 of the 6 still worked), which I jumpered out to make all the lighting the same brightness. I replaced all the bulbs with LEDs and left them in parallel (bad idea, Kirchhoff'* law), with 660 ohms of resistance in the wiring harness to drop the 12 volts. They look good with even brightness, we'll see if and when they start to fail. I am running them considerably darker than with their intended full voltage because of the 660 ohms of resistance, so I may get quite a bit of life out of them.
You can see the original light sensor in my messy test set up on top of the IPM in this picture (top left)
The IPM is on the right with the DIM on the left. You can see my lighting relay behind the DIM.
I added the aux input by interrupting the audio input from the XM module (but the XM module had to be detected, or it will not select it, radio is too smart). Allows me to have the aux cable plugged in and still listen to terrestrial radio, the CD or cassette (unlikely).
A picture of the XM module before I put it up above the hush panel (where the Mitsubishi amplifier had lived since 1984) after initial install when I still reworking and adjusting the stereo mounting bracket.
I had only intended to use the DIM with this setup like older Class 2 units I had read about and researched. The lighting scheme with the ambient light sensor threw a wrench in that, and I really didn't want to fool with regulating the VFD power supply via the dash dimming, since the matched module (VIN) was still available and $10. If only using a DIM in this exact setup, there may not be a VIN match issue, as new DIMs do not require programming. However, it could be a case of the DIM marrying to what else it 'sees' on the first power up, like the XM module allegedly does. The IPM definitely requires programming with the GM Tech II tool.
I had toyed with the idea of using the class 2 bus to implement keyless entry on my car, but it would require the addition of the Driver'* Door Module and the Rear Interface Module (trunk pop), and another door module if I wanted the progressive unlock feature. The GM Tech II tool is also required to match remotes on these series/era cars, though Dorman offers an innovative (limited times usage) tool with replacement remote fobs. Ultimately, I'm not sure this would be worth it. I also risked the wrath of triggering the anti theft system and chime system, which did start chiming (left front speaker) incessantly as I started disconnecting minor components and verifying what they did and didn't do (in between my little 12v battery connects and disconnects) . The car was hit badly enough that the right front door wouldn't fully latch, so it always had a door ajar warning. I don't believe there is a single switch in the car that actually electrically switches anything. They are all low current, discreet signal inputs that feed modules and other modules through the class 2 bus.
The speaker ohms in the original design are odd. The General (in their infinite wisdom) put 6x9 8 ohm speakers in the rear of the LeSabre and 4 ohm 6.5" speakers (I checked a few times in disbelief and against other LeSabres) in the doors with separate tweeters (I believe this was classified as a Concert Sound II or III). I'm running 6x9 three way and new CV 4x6 two ways in the front (all 4 ohm as usual). These stereos (and some of the sister division models) have a simple aluminum plate for the amp heat sink. I had noticed the heat sink heated up quite quickly in operation, so I test fit a Socket A processor heat sink to the plate. I was amazed at being able to shoe horn it into the dash like this!
As you may notice, the connector on the back is rather unusual. This is the Dock and Lock system which is unique to the 2000 - 2005 Bonneville, Aurora, and LeSabre only. The physical attachment of the radio holds it over the fixed connector mounted in the dash. If I could have found a Century, Regal or Rendezvous (had one of these, 2002, incompatible with XM) with this radio, I could have gotten away from the connector and implemented the keyless entry easier. The module system would have pros and cons compared to how I did this one.
The amount of time I have in research and studying bad aftermarket schematics is sad. The XM was kind of an after thought I realized would be pretty awesome. I think it sounds fantastic too! I don't think I could be any happier with it.
If I had found something I didn't think would have looked terrible in the car, even without cost being an issue, I might have gone a different route. Though many people will ask 'why' with an OEM stereo, aftermarket radios just don't look as good to me in old cars as I thought they did when I was young.