Hi all. I'm new to the board.
After getting into lake fishing on a friend's boat, I bought my father in law's boat. 1989 Kingfisher. 1990 Evinrude 115. He's 79 and early stage dementia. He's had the boat forever and kept it in fairly good shape. I've been fishing with him a few times several years ago.

But on purchase and receipt, we've had major issues electrically whereby a new battery is now dead, won't charge, and I'm trying to get my head around it.
I'm 90% sure that when he put in a new main battery a few months ago, he miswired everything. And now the battery's blown along with the charging unit.

As you'll see in the pics, it's a Guest Charge Pro 2631 model. 3 panels 30 amps. The middle panel/lights look to have fritzed with ooze coming from the light casings.
The two trolling motors are in a series and connected correctly for the series.
But the charging wiring looks to be a mess and the culprit for a dead outboard battery, poor amps on trolling battery #2, and a fritzed charging unit.
I thought I would post pics here for your two bits. Pretty ugly?

My guess is the charger shorted and over charged the batteries. Get rid of the charger and have the batteries tested and replace if needed.

I would say the opposite. A shorted cell took out the charger, but at any rate, the charger is toast. I would have the batteries charged and load tested.

First replace the charger and make sure you put the pair of each leed set on the same battery. Just because all three are black doesn’t mean they are common. They are paired that way for a reason. I only see one lead set terminated on the top battery first picture correctly. Second Take a volt meter and see what voltage each battery has and then plug in charger wand read voltage again. Maybe the batteries can be saved.

FYI example only

As Ford it said charger grounds hooked up wrong. Should be hooked up liked diagram

My OCD would force me to clean that all up and start over. Fordnut's diagram is a good place to start. At any rate, that charger is toast. Get a new charger, go have all the batteries tested, and start with a known good setup.

yep, it is definitely hooked up wrong. there should be a red and black to each battery and the leads off the charger should be labelled 1-3. A 3 bank charger will have 3 leads each with a red and black. Each lead goes to a battery.

many chargers are red/black to the inline fuses, then they change to white/black. So, hard to tell from the pictures just exactly what went wrong.

I have seen boats from 30 years ago wired a lot worse than this it. If you take all the charger wiring off and charge the batteries with a manual charger one at a time then check them you will find out if they are good or bad. Then wire the charger back in right and see what it is putting out. Who know it may all be ok if it is wired right.