Need help wiring Fish Finder to Accessory Switch

[NHdeadhead]

hey guys im looking for some advice on wiring a fish finder to an accessory switch. I have a hummingbird Helix 7 that I want to wire in as a second unit but have a few questions/ concerns.

I couldn't get the rocker panel to pull out to access the back of it but underneath my dash I located a set of wires labeled "accessory". There is a red wire for power, a black wire for ground and then a purple with white stripe that must run to the rocker switch. The three wires go into a "3 pin" connector and is capped off. The cap or male of the plug has these little rubber grommets that are removable and it looks to me that you would feed the power and ground wire from the fish finder into the back of the connector and then plug it back in? I have to add a length of wire approx 15' in between the fish finder and the connector. The wire under the dash and the wire on the fish finder seems small like 10-12 gauge? The guy at the parts store sold me 16 gauge wire because it was the smallest they had and an inline fuse. Will that work and do I need the inline fuse? I'm not sure how to connect the wire to the "cap" or male end of the connector, if I remove the rubber grommet I can slide the wire through but it is loose and pulls out easily? So basically I'm not sure if the 16 gauge wire is too big to splice between the smaller wire on the fish finder and then to fit into the male part of the plug that feeds into the same size wire that's on the fish finder or how to make the wire stay in the plug? Sorry if it sounds confusing I'm not great with electrical and trying to get the unit installed before i put my boat in the water for the season

 

[dingbat]

10 and 12 awg wire is not “small” by any standard.

16 awg will take 3A out 15 ft. with 3% drop. Go buy yourself a quality 3 pin sealed connector. Cut the connector off the aux cable and install the new connector

 

[NYBo]

First you need to determine how those wires are powered. They may not go to any switch, and the red may be always hot. The purple/white is likely + for lighting and may be powered through the anchor light circuit.

Isn't there an inline fuse in the wiring harness that came with the fish finder?

EDIT: Where are my manners? Welcome to iBoats! :welcome:

 

[roscoe]

Kind of asking for trouble by connecting helix to unknown wires, from unknown source.
Also, many people having troubles with newer fishfinders like the helix, hook, etc, very sensitive to voltage drop when starting engine and the finder is turned on.
Pain in the butt to have the finder power down every time you start the engine.
In some cases it has been known to lock up the screen.

Suggest you run power directly from the battery, or battery switch if boat has one.
At the very least connect power directly to the fuse block.

And in any case, yes, you need an appropriate sized fuse for that helix.