I run 2 Humminbird units up front. 1 for maps and 1 for 2D/DI sonar. The unit that is for maps only does not have the transducer connected, so there is no interference with the other unit. When you turn on the one that is not hooked up to the sonar, a screen will pop up and say "no transducer detected" and give you 3 options (think it is normal mode, simulation mode, and something else). Just pick normal mode and your maps/GPS will sync up and you are ready to go. Hope this helps.