Dash instrument lights change: semi failure?

Not familiar with the early girls, but the 67/ later, the cluster sort of "hinges" towards you and tips down, then you can slide it clear of the speedo protrusion. If you cannot get the cable loose, "try the other end". Unscrew from the transmission, release the various clips, and work the cable up/ free so you can pull some cable out of the firewall into the passenger compartment