Shop 30 AMP RV Circuit Tester 125V/3750W RV Circuit Analyzer Plug with LED Indicator Light 30 amp Nema TT-30P ETL Listed Surge Protector Circuit Tester Plug for RV Camper Trailer, support 2 Years Warranty with high quality. Together with the diagnostic chart provides LED indication guide for the following wiring condition: Power ON/Correct Wiring, NO Power/Open Hot, Open Ground, Reverse polarity, Open Neutral, Hot/Ground Reverse, Hot/Neutral Reversed with Neutral Open.