My fish finder blew up on sat. It's in for warranty repairs but I was wondering if anyone had any advice on this.

I hooked the fish finder (Lowrance X-51) up to an accesory plug on the throttle & starter control for a 1985 30hp Johnson OB. This came with the boat I just bought. When I tested it in my driveway without the engine running it worked fine. However, on Sat when I started the engine on the water the finder immediately started flickering and acting strange. After a few minutes of running it shut down entirely.

I turned the unit off for the rest of the day. When I got home, I hooked it up to a 12V lantern battery and got nothing. Took it to the shop & hooked it up to the simulator but still got nothing. The 3 ampin-line fuse looks fine.

Anyone heard of anything like this before? When it comes back from Lowrance I am planning to wire it directly to the battery but now I'm worried I am missing something. Might the same thing happen even direct to the battery? It looks like a fairly standard dual-purpose battery.

Thx, Sideoff