Yes you do as the GPS will stay powered up all the time and drain your battery.

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Just hooking this thing up, and i know you have to install a toggle switch from the battery to the sonar unit and also put a inline fuse from the toggle to the unit, but do you have to do the same thing for the gps module. Im just hooking the gps module straight into the depthfinder, so my question is do you have to install a toggle and a inline fuse on the gps line to the unit also??? I dont think so but i have been told by 2 people that you do.
Yes you do as the GPS will stay powered up all the time and drain your battery.
You need the switch on the gps module power supply, the head unit does not need one.
