@boyinneedofhelp How about the the Powerline Led (House Led) on your AV500 main adapter and extender adapter. 

If the House Leds are On, make sure the connection beween router and the main AV500 is fine you could exchange the cable beween router and the main AV600 adapter. 

If the house Leds are OFF,  please add extra powerline unit into existing powerline network by pair button referring to the instruction:
https://www.tp-link.com/support/faq/1081/

Note:  press Pair button only for 1 sec, Power Leds should be flashing on both powerline units in pairing process. ( if the Power Led does not blink, press it for 1 sec again)
When the Powerline Led or House Leds are on, the pairing process is done.