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I know that here most of those without a tach are autos,and all manauls have tachs.
Wrong. I've had 2 manual csm's (colt/summit/mirage) with the 4g15, one with a 5spd and one with a 4spd, neither had tachs until I swapped in a tached cluster. Tach's only came on higher optioned cars such as the es, gl, and gt. The GT has a 145mph/9k tach, others are 125mph/8k however due to it being the highest option available with the 4G61T and turbo body kit (front lip/wing/sideskirts).
Yes, a tached cluster can be "just swapped in" and it will work, all the wiring/etc is all there and hooked up. Find one and stick it in!