I need to get my 72 mustang inspected soon and my backup lights don't work all other lights work so i need some help figuring it out i was told it maybe the neutral safety switch but i have no idea

 

Did you try new bulbs yet? if yes, then you need to get a test light an see if it lights when you select R. from there you narrow it down to NSS. there was a pretty good tech article in Mustangs Monthly on how to change/adjust the NSS