I installed one in my GTX 155 using the included bracket and gel pad, it works perfectly. I did snip off one side of the plastic bracket a little because when checking the fit before epoxying it in I noticed it didn't fit solidly, it would rock a little. After snipping it a little it fit snug against the inside of the hull. Maybe that is why yours isn't working, there maybe an air pocket trapped. Try removing the transponder and reinstalling it.
All this is assuming you are talking about you are seeing the lines when you are in the water.