when i start my motor fish finder on bow shuts off ?????

Swap one of the other matching trolling batteries for the cranking since you have the same ones and see if that fixes it. We are suspect of the battery.

Check your cranking battery while cranking with the kill switch off so you can see what the voltage is while under a load.

Here is how i dealt with the same problem and its helps some. When you turn the key on wait 3-5 sec. before starting the motor. Maybe its the initial surge to power the guages or something but this helped out in my case.

Save your self a headache and pull 2 #12 wires from the battery to the bow and install a in-line fuse on the hot side. I am fighting this problem myself and plan on fixing it this week.