Ran into that on my first trip also. Could also be a bad magnet. Jack one tire up just enough so you can spin the tire, then have someone step on the brake and see what happens. You should hear the magnet and the wheel should stop. All around until you find the culprit. This is after the other tips such as loose connections, check everyone. But from your conversation sounds like something in the connector. Just went through that. Cutting the wifes cardboard nail file to fit into the connector and fill till clean. Blow out the dust and insert for a positive connection.
PS after my first on the road brake issue I now carry with me a set of brake assemblies. Two wires and 4 bolts and its all new again. Along with length of wire and spare bearings and grease. Seems like I always get stuck when Im north of nowhere to be found parts. So now whenever I have an issue with the TT, I buy an extra part and into the storage bin it goes.
