Since we all love cool junkyard swaps, here is one I have recently done and really like.
Many late model GM vehicles have auto dimming rear view mirrors with built in compass and temerature displays. What I found neat about these, are they are "self contained" units. Meaning they are not controlled by the vehicle they are installed in. They only need power, ground, and a temperature sensor to work.
Now there are several different models out there. Some older (late 90's) may have auto dim and compass only, others will have compas and temp. Just look at the buttons on the mirror. If one says mirror and the other says comp, then its compass and auto dim only. If it says comp and temp, then it has both. Some of the older (late 90's) will have a small rectangle window for the display, and will only display temp or compass, not both at the same time, while many newer ones will have a larger square display and read both at the same time.
There are also some later model ones with onstar buttons, you dont really want one of those. Some may also have a display for passenger airbag. So might not want one of those. Just look in all the different vehicles in your junkyards and see what has what. Make sure you get the temperature sensor from the grill of the same vehicle you get the mirror from.
I installed a older single display (will only display comp or temp, not both at the same time) in my 79 cherokee. It fit the stock jeep mirror mounting tab. Ran the wires, mounted the temp probe in the grill and its good to go. This specific one I pulled from a 99 chevy suburban.
Now for my YJ I scored a newer one with the larger display that will read both temp and compass at the same time. This specific one I pulled from a 03 saturn vue. I also got the mounting tab off the glass. The windshield in the vue was already cracked from the wreck, so I just used a stiff putty knife to remove the tab from the glass. It knocked out a chunk of glass with it. I used a heat gun once I got home and removed the glass and glue from the tab.
Mirror and temp probe:
Some google searching got the pinout for the wires. Yellow is power, black is ground, and the green/blk and grey wires go to the temp probe. Any other wires can be removed. I only had 1 that I removed.
So now to get the jeep mounting tab off the glass without breaking my windshield. I took a heat gun and worked it over the windshield to heat it up and kept it warm and then heated up the tab and used a thin razer blade and it poped right on off. Cleaned the glass and tab, and glued on the tab for the new mirror.
Now to wire it up. The wires are real small as the mirror draws very little power. I actually used some 18 ga speaker wire and even it was larger than the mirror wires. I ran two down the right side, and the other two down the left side. I ran the wires under the rubber moulding around the glass and down the sides of the dash. You can see the wires on the side, but it doesnt bother me. Hooked up the ground, and the power to a switched 12v source.
Now for the temp probe. Its a funky little thing, made to snap into a 7/16 hole. So I used a peice of thin scrap metal I had and made a bracket for it. I used a 7/16 washer to take up the extra room, as it was ment to snap into a thick peice of plastic.
I ended up deciding to mount it in the drivers fenderwell, I started to mount it in the grill, but it can pick up on heat from the radiator if not moving fast. Also in the fenderwell it mostly shaded from direct sunlight so maybey it will get a better temp reading. I just used one of the fender to grill bolts. Should still have plenty of air flow and the sensor and connector are both waterproof, so no worries about rain.
All hooked up and working. Ignore the "cal" It just needed to be driven in a circle a few times to calibrate the compass. I took the pic before I drove it.
Hope everyone enjoyed the mini writeup. Any questions I will try and answer them.