Hi Brad,
I'm not Dad's 50 but with the sender out and not connected to anything, you hook one lead from your ohmmeter to the center terminal and the other lead to the body of the sender (one of the mounting holes will work). with your meter on the ohms scale you should see the meter go from 0 ohms to about 30 ohms when you move the arm. it doesn't matter which meter lead you use for either connection because you are just measuring resistance which is not polarity sensitive. Hope that helps.
Best regards,
Les
