Any idea of what kind of motor home, make, model, year, engine, trans, diesel, gas? Some of this might help in trying to aid you with an answer. You see, many speedos are controlled by Vehicle Data computers but, those are only on certain models.
Scott
Scott and Karla SDFD RETIRED2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing KI60ND