I checked my Owner's Manual for the 1986 420sel,560sel and 560sec. It lists an outside temperature sensor located directly below the speedometer. Of course mine is broken. It is a LCD that constantly reads 5(smeared second digit) and hopefully I find a donor car at a junkyard this spring. Goodluck!
1986 420SEL. 200,000 miles plus.
1991 Cutlass Supreme
1980 VW Vanagon (Old Smokey)