This past weekend I installed a Garmin Striker 4 fishfinder. I wanted to use one of the two unused accessory switches. I used a multimeter to check all of the unused connections. Two up front, underneath on the port and starboard sides, two under the helm and one aft, near the port side. With the switches on I could not get a reading on the multimeter. I did find a third connection under the helm near the radio. This connection was on the radio circuit. I didn’t want to add the fishfinder to this circuit. I wanted to put it on its own circuit but time was short, it was raining and I was trying to do this by myself so I ended up using the (3rd) accessory switch with the radio on the circuit. My guesses why I couldn’t get a reading on the multimeter is that 1, the connections were corroded or oxidized enough that I could get a good contact with the probes. 2, the circuits were not complete. I tried to trace wires but it just became too time consuming. I plan to revisit this at some point. Any thoughts and suggestions on why I couldn’t get a reading and what I could to make this easier?