Thanks to Andrew WK of Audiworld for this.
I decided to go ahead and put together some information for everyone on integrating an aftermarket head unit using the Metra harness. This is using a 1995 S6 Avant with Gamma head unit as an example. I’ve found alot of FUD regarding integration with the stock Bose components, so I figured it was time to layout the facts.
What you need:
1. Metra 70-1785 harness (for easy connection to Audi harnesses)
2. Head unit with 4x >2.2v preamp outputs (for the Bose amp connections)
3. 2x ground loop isolators (prevents popping on track change)
4. High quality crimp tool (for wiring the Metra to your HU harness)
5. 5x Insulated crimp caps 14-18gauge (for the wiring connections)
6. Audi radio removal tools for your car (to get your radio out)
Head unit suggestions:
1. 4x preamp outputs of 4v
2. ability to turnoff internal amp
3. time-delay configuration for each channel
Some key points to note. You will need to wire your power antenna/remote amp trigger connection to turn on/off the Bose amps with the head unit. The GLI’s (ground loop isolators) are connected between the LF/RF/LR/RR pre-amp outputs and the harness connections to each channel on the Bose amps. The GLI’s will eliminate the pop when changing tracks by preventing a discharge of the Bose amps, as modern stereos don’t use common ground. I got a pair from Bestbuy that seem to do a great job. Here’s a picture of the GLI’s installed with the Metra harness (this is a 2-piece harness):
Only 5 connections in the bottom double Metra harness will be used. They are constant +12v (battery), switched +12v (ignition), illumination, Amp Trigger and Ground. I have also labeled a photo of the harness below. Make sure you twist your wire connections tightly. You can solder them too, if you like. Here is a labeled photo of the diagram on the Gamma unit to show exactly which connections are used for the installation:
Backside photo of the 2nd piece of the Metra harness. I removed all the extra wires that weren’t needed.
I’ve built harnesses for a Kenwood with 2.5v pre-amps and the Alpine CDA-9887, which I’m currently using. They both sound excellent with no popping ever (my stock gamma in both cars used to pop occasionally on track changes). The Alpine sounds far superior to the Gamma, especially after configuring balance/fade and the time delay for each channel. I want to try out the Alpine Imprint sound tuning kit with the Bose components. I will update this after I Imprint tune the system to let you know how things turn out, as of right now I see no need to do a Bosectomy. Here’s a finished shot (ignore dust):
The head unit fits perfectly, as the gamma uses a standard sized opening. It just slides right in and maintains a tight pressure fit. You can use the Crutchfield car configuration function to determine stereos that will fit this opening. I’ve tried to include everything, feel free to post any comments or questions and I’ll update accordingly. See my picposter for a few extra photos of stuff.
