Oil pressure gauge not working on 71 Demon rally guages

I took the Demon out this morning for a spin and noticed the oil pressure guage needle not moving at all. I will tackle this later but need to know what are the logical steps to troubleshoot this problem.Can the sending unit be checked on the engine to see if it is working properly sending signal to gauge? Can the gauge itself be checked without pulling cluster. I want to try to fix this myself to save some bucks and learn more about fixing my car. Thanks for your help.