Before you go buying parts, pull the rheostat connector and check for power there. If it's not present, you likely have a blown fuse or something along those lines. If there is power, then turn the rheostat to full bright and look for power on the other side of it by backprobing the connector. That way you can test it. It's also possible that you have a bulb problem in your instrument cluster. Throwing parts at it does nothing but waste time and money. Diagnose, then replace.