Should work fine as long as the K number is the same. Sedans and wagons have different numbers of counts due to different tire diameters. Actually the speedo will work fine, just may read off by 10% or so.

Sedans should have a K10042, wagons a K9800. Later ones for ABS equipped cars have different numbers, which are 4X the older numbers. (K40168, K39200)

You'll find a connection for the service light on the 1990 speedo; you can just ignore that connection when using it in an 86. That's a pair of wires across the top of the speedo to a mechanism on the side opposite the silver drive motor. Not needed for 86-87 cars which have no useless "SERVICE" light.
--
::: Rob Bareiss, New London CT ::: 92 244 ::: 90 745GL ::: 90 745T ::: 84 242DL ::: 90 745T Parts ::: Used to have : 86 244DL, 87 244DL, 91 244, 88 244GL, 88 744GLE, 82 245T, 86 244DL, 87 244DL, 88 245DL, 89 244DL!