Q: Speedometer light does not work but all other dash lights do. The bulb is good

When you have cluster back exposed you need to recheck the bulb sockets and bulbs and test contacts for bulbs to make sure they get power and ground. The other lights and speedo and rpm gauges all use same circuit board and most likely light socket and or the circuit board on cluster is bad.

On a speedometer unit such as this with bulbs that can be replaced, they usually just twist into the cluster itself and do not have any wiring Associated directly with the bulb itself like a tail light or a headlight would. The bulbs connect directly to the cluster and then there are a couple of connector spots where the wires connect to all in one place. The cluster itself acts as a motherboard for electrical function. It is possible that the bulb for those gauges could have a poor ground or poor connection of some kind to the cluster itself. I would recommend replacing the cluster to resolve this issue.