BigBendFishing.Net

i have 2 batteries and a battery switch, (1,2, both)
when i use #2 battery and start the motor the gps turns off, this does not happen when i am using #1 battery, could this be a ground problem?

Most likely a grounding problem. Are both batteries grouded to your electrical relay board? Repair or replace the cable on your defective battery. Thoroughly clean your battery terminals,check and tighten all cables.

thanks
i will check it