i rewired my boat trailer, but it down work. did just what the instructions said to do. have good ground to trailer, even added additional ground to each taillight b/c it didn't work. got a tester for truck trailer hook up at Wal-Mart and only show that i have power to one of three probes. checked fuses and they appeared to be fine. I'm driving a 2010 dodgeram 1500. worked fine on old trailer but not on either trailer now. please help, want to go fishing.

 

You need to start from the beginning.
You say the fuses appear to be good. I would use your multi meter to be sure. Do a continuity test to all the fuses related to the trailer lights.

You truck will have turn signal fuses. Brake fuses, Tail light fuses. If your truck lights are working? Don't bother checking.
Your truck may have Trailer turn signal fuses, Trailer Brake fuses, Trailer Tail Lights. And Trailer Light Relays. Test all these on confirming performance move onto the back bumper. Using your multimeter test each circuit to insure power is reaching the plug.

Once you have confirmed this... You will know the problem must be in the trailer.