The backup camera display is fastened to the vent with an elastic stretch. I unscrewed the display cover, put some stretch behind, screwed the cover back, and hooked the stretch to the vent. It took me a few minutes, but the connection is very firm.
Power is taken from the Scan Gauge II cable. I found ground and 12+ wires, made a small cut in the SGII cable (not to damage other wires), and soldered a 2.5mm audio jack. (you can use 3.5mm jack - I wanted to make it all small so 2.5mm). The display is connected through a very short cable with a 2.5mm plug.
For the camera, I bought a trailer plug. I cut the top to make it flat and glued the camera to it. The trailer backup lamp connection didn't work, so it had to be fixed by GMC service.
BTW, you can solder the display directly to the SGII cable. I didn't do it because it wasn't sure how it was going to work out. Now, I see everything works very well.
Small problems: the camera display is powered even when the car is off (picture only when backing up). Not a big deal. ScanGaugeII has an auto shut down.
There are some interferences when backing up. Likely, it can be improved by moving the camera antenna. I don't care about it much because I use it to verify that nothing is behind the car. After that, I do the standard backup maneuver.
The camera around $100 at Walmart. If you want to buy ScanGaugeII, I think it is around $160-170 - check the website (I bought it at a small, local retail store). Mio P550 was around $300 at Buy.com. P550 is not perfect, but good enough and it has lots of POIs.
The Scanguage is interesting. It seems like most of the features can be read of the DIC, though. Are the numbers the same? I'm curious what MPH would be displayed between this device, the speedometer, and the HUD?
Looks like it can be had for $160 shipped on Ebay:
1. ScanGauge has 10s of different features. Much more than DIC. For example, MPG current, average today, average this trip, average tank etc. Although, novelty wears off after a while (like with almost everything). I got it because I don't have DIC. I use it to review current MPG. Once a while, I look at speed: digital value is easier/faster to read.
2. MPH from ScanGauge is exactly same as the analog speedometer. The car analog speedometer may be a combination of digital/analog and they may get the speed value from the same source.