1969 Dodge Dart Gt temp gauge and fuel gauge not woriking

Could someone please help me to figure out where and how to start finding out why my fuel gauge and temp gauge does not work on my 1969 Dart. I don't know if it's the sending units or the instrument cluster itself. I don't really know where to start. If I can't fix the problem where should I take the car or just take out the instrument panel and have it rebuilt. Any suggestions will be greatly appreciated. Thanks for any and all help.