I am not an electrical engineer but I checked the voltage coming from the loop detector and the dvd player and they did not have any. I guess the loop detector maybe just completes the loop of something else? I am not sure I will need to read about the detector.
But the test worked great. I hooked the play switch directly to the loop detector’s car presence. It will turn on the dvd player. What I like about this dvd player it the play button just plays and does not pause also. Pausing would be bad. So with this dvd player it would play the message all the way through and then reset to the beginning of the dvd. I will need to test more on the dvd player and find a speaker to play the message.