we have a humminbird 597C at the bow of the boat and everytime we turn off the big motor the unit also turns off. we have to turn the master power switch off then back on, then go to the front to turn the unit back on. What would be causing this? Wiring issue?

Check the voltage at the bow where it connects into the 597C. I had a similar issue in the past where the wire feeding it was shorting out; not a complete short, but was just enough to drop the voltage to under 12V. Some units shut down if the voltage is below a certain value.

You can also troubleshoot by running a new wire directly from the battery to the 597C to see if it powers on without the big motor. If it does, replace the wiring with new. Good luck

check your grounding, bad grounds cause all kinds of electrical gremlins

Whenever I have power issues with a big item like a fish finder I usually just run my own power wire to the battery and eliminate any doubt...

Post in general equipment

Is it connected directly to the battery, not connected into the existing wiring? It should be run direct to the battery alone and have a fuse.

Did you upgrade the wiring to a heavier gauge? The extra length for the bow unit, should bump it up from what you needed for the console.

Is the battery fully charge and in good condition? If it was getting weak, it could cause it but more than likely it is the wiring to the unit itself

if this is a new problem it sounds like a weak battery. if I understand your problem with engine running and you turn it off you will have a voltage drop because you were running on a higher alternator voltage. I had a similar problem a year ago. good luck. let us know what you find.