ok , if the rb24 speedo is still running off the rb24 gearbox there shouldn't be an issue , i would be inclined to say your speedo cable is broken (which is quite common if it's the same as rb20) . rb20 cefiro uses a r32 speedo cable , it has a little plastic end glued(?) onto the cable , simple fix is to pull your cluster out and glue the end back into the cable (there is a thread somewhere on sau , but i think it was for r32 which is the same). as for the wiring , i'd advise you speak to an importer to see if they have a half cut you can get the complete under dash loom from (or order a rb25det a31 half cut if your after a rb25 and gearbox)