HB recommends 14gauge ....12gauge is better ... I use 10gauge ...
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To connect HELIX and 898 you will need AS EC QDE adapter cable for the HELIX (898 is direct connect) ...
https://humminbird.johnsonoutdoors.c...-adapter-cable

And an Ethernet cable long enough to reach ...
https://humminbird.johnsonoutdoors.c...facets=7319%2C
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AS GPS HS antenna will connect directly to either head unit ... and can then be shared to the other head unit thru Ethernet ...

Rickie