On 76 sov. Airstream used entire dif. than standard trailer end, as far as I know they didn't start to use standard until later years. The way to tell what each prong is to take 12 volt
bat. ground to trailer hot wire from bat to each prong to see what works or ground tow vehicle plug to trailer then wire from tv plug to see which prong matches. I have diagram but is in storage for winter, owners manual will also show correct wiring. If plugs are to corroded take back off trailer plug then terminals are easy to see.