I have a 1989 organizer bass boat it has a trickle charger in the back. I replaced the trolling motor batteries it has a switch at the front that checks battery life and can be switched to charge. Maybe a stupid question but how does this work? Does the trickle charger need to be plugged in I have never had a boat with so many options usually just charged all 3 batteries individually thanks for the help
I wish there was a simple answer. If none of the wiring has been messed with then the switch should link the 2 trolling batteries in to parallel (12v) at the trolling plug. Then you plug a battery charger into the trolling plug. The idea back in 1989 was to allow you to charge the trolling batteries with out leaving the rear door open on the boat and to avoid having to remove the batteries to charge. The starting battery should be charged by the motor so there was never really a option to charge that one.
The best modern option is to forget about the old system and buy a 3 bank onboard isolated output charger (about $160) then just plug a drop cord into the receptacle on the boat and forget about it. All 3 batteries will charge and look after themselves. You could go with a cheaper 2 bank and only recharge the trolling motor as the main starting battery should be kept charged by the motor but the 3 bank is only slightly more expensive so its worth the extra 20 bucks.
As Alldodge said above. If you want to restore or make the system work just post a few diagrams or pictures of the wiring and switches and im sure it can be figured out