Mercruiser 470 170 HP 1986 Seville dual battery bank

[kastengeist]

The boat is draining the battery system after about 20 or so minutes on the water with no accessories running. This is my buddies boat. He wants to have two batteries for start and 2 batteries for accessories. So 2 in parallel for each. I am not sure how to separate the system I have the book and see the hot wire is a pink or red / blue and I see the purple wire which I think is tied to the coil but I am a bit lost on what to do. I am thinking the electrical system is dying because of corrosion and or a short some where plus there is no alternator, however he is looking to get one. I did here of a bracket for a universal alternator but not sure where to find it. The batteries currently look to all be in parallel but the starter is connected directly to the first battery and there is a switch that connects battery one and 2 but on the common side I have a thick red wire and cant see where that goes and can only assume maybe it hooks to the breaker and a orange wire with a fuse that seems to possibly go to a bilge pump.

 

[Silvertip]

From your description there is no way anyone can tell you WHY the batteries are going flat. And since we have no idea how they are wired now (dual battery switch yes or no) that also complicates things. One bad battery can suck all the other dry if they are all in parallel. Are all the batteries "good" (meaning will they hold a charge if fully charged). Have them load tested to be sure. There should be no direct battery connection to the coil. And yes -- you have an alternator -- it is just not a traditional round belt driven style but rather a stator design much like an outboard. To make a "general" suggestion, you put two batteries in parallel to create two sets of two batteries. You keep the two sets separate bit each set connects to a dual battery switch. The COM terminal on the dual battery switch then feeds the boat and engine circuits. The ground terminals from both sets of batteries get connected together and then connect to the engine block. All cables must be the same size as the normal battery to engine cables.