My 120 MPH speedometer in my 88 Formula just took a dump. I have an 80 MPH speedometer here and was wondering if I could plug it in and go paly. Thanks in advance.

I haven't done it, so take my advice with a grain of salt. According to the service manual and the parts book, the same speed sensors and wiring up to the speedo are used in all Fieros, so the calibration must be done by the speedo itself. That means you should be able to swap one or the other in and it will work as it should. Regardless, no harm will be done if you try it.

Plug and Play even if it's Metric.

The change is in the speedometer itself, they all get the same number of pulses per mile, or per Kilometer if it's Metric. (Metric dial shows 140Kph for about 85Mph)

If you change the diameter of the tires then any one would be in need of calibration.

Tire size calibration is only done at gear on VSS or electronic between VSS and buffer for speedo and ECM. (Fiero buffer is in speedo.) Speedo and ECM/PCM needs accurate MPH.

Yes, all Fiero speedometer is plug and play. No dif to car...

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

I went from a 85 mph speedo to a 120 speedo. No issue. Plug and play.