How do I Bench test 73 Swinger gauge cluster

I would start at the cluster and work my way back. So find the pin on the back of the cluster that feeds the lights (there are only 3 illumination lights on the cluster) , it should be the fourth pin from the gap starting at the bottom. Ground your dash and put 12V on that pin and see if you have light. If you do then there is nothing wrong with your cluster (as far as lighting up goes). The next step would be to check all the connections going through your switch. I don't have the steps for that but it should be fairly easy with a voltmeter.