Speedster 200 Dash issue

[shore]

07 200, twin 430hp.

Here's the rundown, it's a boat I'm looking at but developed an issue prior to me going to look at it so I can only tell you what I know.

Main battery went down. Battery replaced. Stereo started to hum and gauges/stereo went out. Both engines run as normal.

computer?

fuse box corroded?

ground not hooked up?

 

[VERDUGO135]

If its the same as my 08 the battery has 3 grounds. One for each engine and a small wire that sends low current ground to your dash, radio, and accessories. I was going crazy trying to figure it out til I found the wire hiding behind the battery unhooked.