KJ
Could be the Switch has some corrosion on the #2 Position contacts. Changing the switch is about the only solution for that since the switch is sealed and can't be effectively cleaned.
Before you change the switch check your battery terminal connectionss to assure they are clean. Corrosion adds resistance to the circuit and that can make a switch problem seem worse than it really is.
The Sonar shuts off when you crank the engine:
Your starter draws a lot of Amps / Current when engaged in starting the engine. It's possible your Battery is getting old or the engine wire terminals may just need cleaning. Also check to make sure the terminal Wing Nuts are tight..loose wires will cause added resistance due to arcing.
One other thing to check is the battery size:
If you run all your accessories of the cranking battery you may need a larger size. It's common for maunfacturers to put a Group 24 Battery on the cranking side. It's cheaper for them to rig the boat that way. They work fine for a while but due to excessive Amp load cycling rates they dont last as long as a group 27.
If you have a Group 24 try going up to a Group 27 Cranking Battery for more Amp Hour storage. You may just be putting too much load on an undersized battery.
Bazz
