The dealer wants hugh $$$ for this install because they say you "need" to replace the trucks wiring harness.
I installed the overhead compass/thermometer on my truck, that was not factory equipped, because I wanted the clean factory look and I find the outside air temp very useful.
I looked at other alternatives and the other option I was considering was the light sensitive rearview mirror with the temp/compass. The mirror was $250 + a few extra bucks for the harness. I think it would have looked nice and been functional. but I didn't like the price for what seem like such little conviencience.
So I found a factory O/H console from a salvage yard that had the comp/temp in it. I also got the light sensitive mirror and the wiring harness from the same wrecked truck. The truck I got the parts from no longer had the factory temp sensor (it had been cut off) so instead of looking all over hell I decided to get a new one at the dealer.
I think I paid $50 for the O/H console with the harness, $5 for the mirror, and the snesor was $17 at the dealer.
The install was very easy once I sat down with the manual for a while and mapped out all my wiring connections. Removing the headliner and A-Pillar helped with running the wires, but I don't think you have to do it. The actual install of the console and completing all the wiring connections prolly took me less than 2 hours.
If you need more info or have any questions just drop me an email. If you plan in trying the install let me know and I can send you the wiring schematic that I came up with.
-Ryan