Sounds like a grounding problem to me and you are still hot on one or more of the wires. What kind of downriggers are you using? Ball, snaps, SS Wire? All these items effect the wires. Also, I assume that you checked out the boat(?)

I am a firm believer in the Box. My catch rate has tremendously improved over the last few years. Keep in mind the voltages listed are recommendations. It takes a little tweeking to find out what voltage is best for your boat.

Lastly, a cheaper version of the Box can be purchased at Cabela's. Here's is the link for the Cabela's Box and useful info about it (same info on the Scotty website however, it is currently down). I don't know anyone who has the Cabela's Box, but I imagine it works as well as the Scotty. Hope this helps!

Downriggin'
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"If you are not scratchin bottom, you ain't fishing deep enough!" -DR

Puget Sound Anglers, Gig Harbor Chapter