need help connecting the batteries in 1979 sea ray 300

[jimn]

Hell: I sure could use some help to understand how the three battery, two switch setup in the 1979 searay functions. I was assuming the two batteries ran the motors and the third was for the dc accessories, but, this does not prove true, at least in my experience. Please can someone explain the theory of operation to me. I have two switches, one switch is on/off. The other switch is 1/both/2/off. Two of the three batteries have a jumper to connect their negative posts. Thanks Jimn

 

[MrDough]

Well, I don't know the specifics of your boat but you might have have two batteries as the house batteries to run your electronics when your engines are off; the other is probably your starting battery. Normally the I,II, Both switch allows you to switch from starting battery (the third) to, in case of emergencies, the house batteries to start the engines. Your I, II, Both switch should be on the one with the starting battery most of the time.

The two batteries with their negative posts jumped are probably set up in parallel (the positives probably hook up together at the I,II, Both switch). This is a good indicator they are house batteries as this method increases the amp hours.

Only way to know is to trace the wires from the battery to see what terminals they go to

 

[andyr]

I have an 89 300 and mine are as follows. One battery is connected to the on/off switch. Call it bat 1. This battery is connected to the port engine and port ground and port drive and port alternator. Only the engine is run off this battery. This battery is aft most. The other two batteries are connected to the 1 both 2 swich and stbd engine, drive, all lights and 12v accessories. This way if you run down those batteries, you can always start the port off bat 1. Nothing else draws on it. You may have an emergency start switch on your helm. It crosses the power from bat 1 to the 1/2 bank or the opposite way if pushed the opposite direction. There should be a neg bat cable connecting the 1 bat to the 1/2 bank. This way after port is running you can cross it over to start stbd. This way you can also run down a battery in the 1/2 bank, then switch to the other to run down and still have a battery fresh to star. I normally leave the 1/2 on both though. It is a very good system keeping one engine independent.