speedometer/speed sensor problem

If the cluster was used, what year did you get it out of specifically? This is important. Even though SN-95's have nearly identical looking gauge clusters, there are many electrical differences. An example of this, you cannot use a gauge cluster from a GT in a V6 model without doing a few modifications. Does the new cluster read 120MPH or 150 MPH? If it's 150, then you have one from a GT...or at least the 94-95 GT. You CAN use the Speedo from the GT cluster... just carefully unplyg it from the PCB socket and swap it out on to your own. It will work fine that way.

There's also a chance that the speedo isn't your problem. Does anything else appear to not be working ? Lights...gauges door chime? Theres a fuse that controls some of the gauges and EEC relays... etc.