How to check a backup switch

Hey all I have a 67 notchback that can’t seem to figure out why the backup lights won’t stay on. It is a four speed and curious it might be the switch in the trans. How to do you check to see if it is working correctly. The lights come on than go out I want to at least be able to start with this switch and work my way back through the rest of the system
Thanks in advance
Pat Faley
East Peoria IL
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