How would I make the tach of the turbocoupe cluster work on my 88 cougar? Also is the speedometer just plug and play?
You've got to run a wire from the ignition coil to the cluster, as the base cars do not have the tach wire in the harness. The tach can be modified to be accurate with an 8-cyl by following these instructions:
http://www.coolcats.net/tech/advanced/4to8tach.html
You'll also have to replace the oil pressure sender with one from a car with a gauge (Mustang GT) and you'll need an extension for it to fit - the oil filter will get in the way otherwise
The speedo is "plug and play" in the sense that it will not need to be recalibrated or anything like that, but you'll have to re-pin the harness connector so all of the circuits are in the correct positions