Not long ago, I bought a mirror on ebay from an HHR with map/dome lights, OnStar, auto dimming, compass, and - I thought - outside temp display. It turns out that even though the characters "°F" and "°C" are there in the VFD, they don't even light when you power it up.
Still, because I had bought the mirror and went to the trouble of integrating an RJ-11 jack for my radar detector, I decided to try and get the temp to display in the DIC as well. That was an entirely different rabbit hole...
Once I gave up on getting the temp display in the DIC, I went ahead and got another mirror from e-bay. This time, it was from an '05-ish VUE, with OnStar, auto dim, compass AND temp... but no map lights. That meant if I wanted map lights, I would have to work them in myself (in addition to the RJ-11 jack. again). When all was said and done, I took the map lights from the HHR mirror and made room for them in the VUE mirror. That was easier than taking the map lights out of the stock Solstice OnStar mirror. The cool thing was that the map light board on the HHR mirror has a 3-pin female molex plug to mate with the main circuit board. The main circuit board in the VUE mirror, as it turns out, had a matching 3-pin male plug that is apparently used for an OnStar microphone if the mic is integrated into the mirror (which it isn't in the VUE). That meant that two pins on the main mirror connector (16-pin that you plug into the back of the mirror) already lead to that microphone connector in the VUE mirror. I only had to make a jumper for the third pin and I was able to plug the map lights into that. Maybe the following pictures will explain better than my words:
map light board from HHR mirror (they're already LED's)
HHR mirror main board (the 3 tube thing, I think is for the compass - better than the clunky dongle that hangs off the VUE mirror 
)
VUE mirror circuit board (microphone plug socket circled in black)
jumper
Once the wiring provisions were done, a little dremel surgery was necessary to make room for the map lights. I was just a little bit off with one of my holes, but unless you're looking at the bottom of the mirror, you'd never know it.
Speaking of wiring, there were several other pins that needed to be populated in that 16-pin connector. Here's how mine breaks out now:
1 - Courtesy lamp low control (dome light signal from BCM)
2 - ground for map lights (jumpered to pin 8)
3 - empty
4 - empty
5 - empty
6 - outside temp probe signal
7 - outside temp probe return
8 - Ground
9 - +12V reverse lights signal (turns off auto dimming in reverse)
10- +12V for map lights (originally blue/white wire in pin 6 on solstice mirror)
11- OnStar Keypad signal
12- OnStar Keypad supply voltage
13- +12V ignition
14- OnStar Keypad green LED signal
15- OnStar Keypad red LED signal
16- empty
I hacked the stock mirror to bits to use for another project. I'll post that one up when I get a chance.
