We had a problem on our boat and it was driving my husband crazy. Apparently some new device he bought, a gps plotter, didn't work as expected and he spent a lot of time getting it to work. Explored blogs and fora on the internet, checked all the wiring over and over again and he even took it out of the boat and made a test at home, connecting it to an old car battery. At home it all worked. Eventually he found the cause of the problem and it was the position of the gps antenna. Apparently that thing could not work directly next to another antenna he has on board for some other device. He was happy.