Once you get your battery charged and installed in the Pup again, you can use a jumper wire at the plug to test the trailer lights. Simply jump from the 12V charging pin (4) to pin 3 to test the tail/running lights, then to pin 5 to test the left turn/stop light, and then to pin 6 to test the right turn/stop light. If the lights illuminate, you know the problem is with the tow vehicle/tow vehicle plug. No lights and you know the problem is with the Pup and can start tracing it from there.
Before starting the tests, be sure to check that the ground wire for the Pup's battery is securely connected to the Pup. Loose or corroded ground wires can cause all kinds of weird things to happen.
