I just installed a factory 1999 and up one that displays temp and compass at the same time. The OBS, 88-98, display one or the other; and some only compass even though you can see the F and C in them. All of them auto dim, which is the best feature of all, highly underrated.
Between those two breaks in years are two different sensors so be careful.
88-98 sensor and mirror:
http://cgi.ebay.com/ebaymotors/Chev...r_Truck_Parts_Accessories?hash=item27ad43bf11
99 & Up sensor only:
http://paceperformance.com/index.asp?PageAction=VIEWPROD&ProdID=221604
The wires come with up to seven wires or as few as three:
3 wires = compass only
7 wires = compass, temp, auto dimming side view mirrors and reverse override of dimming
If needed I can get the different part numbers for you, but best to just find all in a junkyard. All are made by a company called gentex even most of the aftermarket.
To just run compass and temp with out the dimming mirrors you will need the following:
ingnition
ground
+ temp probe
- teimp probe
The temp probe is mounted directly behind the grille on all vehicles I have seen. The wires to it are brown and green/black. The sensors are the used in all GM vehicles but be aware of the mirror year and sensor type needed. For example my mirror is from an '01 Tahoe and my sensor from a saturn, totaling 25$ at the local jy.
-Alex