Okay, time to give this a "Wrap Up"... I hate unfinished threads and you don't know how it all turned out.
The screws on the Garmin are T3 Torx, and they are made out of Aluminum.
The screw head mangles easily if you try to push too hard on the Torx screwdriver and it is not quite lined up right.
I really would have enjoyed all brand new screws to put it back together, but time has run out, and I need this done today....
So, I put the old screws back in about half-way. More than that, the case gets messed up, so I quit. The back of the GPS case "Snaps Together" anyway... so I can only assume the screws are there to prevent the case from snapping off from a windshield mount on a hard bump.....
but, I had to use special cellphone tools to get that case open, even with the screws removed... this is overkill on Garmin's part.
The new audio cable is installed, I left 4 inches outside the case with a molded jack on the end of the cable. Looks great, works fantastic. The audio level from the voice coil of the GPS speaker can easily over drive the bike's intercom.... the first time I heard it, it almost took my head off. I reset the GPS volume to 50% and that was much better.
One Comment: The audio cable I used is a Stereo Cable. I twisted both leads together and soldered them to the speaker voice coil. I was not a 100% sure which lead that the Intecom Adapter would use, most likely the "tip" but I made sure both the "tip" and the "ring" terminals would have audio.
The Sierra Electronics interface also has a volume control. It was set at mid-range, I backed that off to 25% and now things sound very smooth from the GPS.
The truckers where having a holiday on Channel 19, and the GPS muted them perfectly.
I am a happy camper.... Going to Miami, OK tomorrow to visit with LtDan282 whom I have not seen in several months.
Here are a couple of pictures showing how my audio cable install went.
I drilled a hole thru the back of the case adjacent to the speaker's terminals. The hole is in a trough between the battery and the speaker's housing. The cable insulation sticks thru about 3/8 inch. I used E-6000 flexible clear cement to keep that cable from being pulled back out of the GPS case.
and here is how I attached the wires to the speaker.
So, 33 in newsprint code, it is a wrap.