What brand is it? If it’s Raymarine, you can find detailed information online regarding voltage readings, which are easy to check with a multi meter. Two place to check are at the mast jumper and the display head. You can also call Raymarine for technical help.
If your area in NJ is anything line up here in Ma, getting an electronics guy to come out an having a look any time of year is like hitting the lottery.
I think in my next life I’m coming back as a Marine Electronics Tech.