There are three different OEM '87-'93 140 MPH speedometers:
'87-early '89 SSP
late '89 5.0L non-SSP
'90-'93 5.0L non-SSP
Yes, you can get a 90-'93 speedometer to fit in an '87-'89 cluster. But the mounting points are not the same. See the pictures posted above. Notice the placement of the holes at the top and bottom of each speedometer face. OR you could just get the proper late '89 non-SSP speedometer or cluster, or an '87-'89 SSP speedometer or cluster.
As I posted previously, the '90-'93 cluster harnesses are not wired the same as '87-'89. There are about a half-dozen wires that are in different locations bwteeen the two harnesses. If you want to put a '90-'93 cluster in an '87-'89, you have to moves wires from one harness to the other, and vice versa. You'll need wiring diagrams for both clusters to know which wires to switch between the two.
1979-1993 Fox Capri and Mustang VIN Decoder: foxchassis.com
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