Does the speedo function reliably otherwise? It's very important since you may just have a working speedo and a working speed sensor but the speedo is calibrated for different rear end ratio (or somesuch in effect).

1. What did the previous speedo do (before you replaced it). Was it dead? Were readings steady or intermittent? Whenever the reading would be there, was it correct or some percentage of the actual speed?

2. Does the replaced speedo do exactly the same thing as the one before replacement?

3. Does the trip meter work correctly? Find a stretch of highway with half-mile marks on it, or just use a decent map, gps if you have one or simply mapquest to figure how long a way it is before two strategically chosen intersections on a straight road nearby. Then just zero it at one point and read it after driving the distance you know from your chosen source.

Cheers, Kuba