Anybody know where there is a wiring diagram for a single engine boat with four batteries (Two optima red top starting batteries, and two optima yellow top dual purpose batteries) using a Perko 1/2/both/off switch?

i’ve tried the Perko website, but they don’t show a 4 battery set up

I'd use 3 Perko batt switches and wire it this way.

That seems like a lot of extra connections. I only have one Perko switch, and really only want to use one. Does somebody have a detailed wiring diagram using only one Perko switch? Need to know exactly which negative and which positive to connect to each other. Thanks

So, you want to hook two batteries together to keep 12 volts but double the capacity ?

Also, better to explain to us exactly what you want these batteries to do.
example: one pair for starting only or mostly and one for deep cycle needs like stereo on while engine is off ? Or ?

Yes, I’m looking to have two “sets” of batteries. Meaning two batteries to run the stereo, and two for starting. But then with the Perko 1/2/all/off switch be able to use all the batteries to start the engine if needed.

I understand the general concept of this, but need to know exactly how to hook up the positive and negative wires to achieve it

You should be fine with just one start bat, but if you want 2 each ok
Don't know how you plan to recharge the house bats but drew one up with an ACR

Having 2 batts connected in parallel works great for delivering current, but when charging it can cause problems.. If one batt reaches VR cut-off, the other battery is left not fully charged. An automatic battery isolator is needed to allow both batteries to be fully charged. The additional Perko batt switches would allow manual control of charging eliminating the need for battery isolators. If you plan on re-charging the house batts only at home (independently), you could eliminate one of the Perko switches (for house batts). If you decide one starting batt is enough, you could run with just one Perko switch that would be selected to house batts or start batt. My orig drawing would allow any single batt to be fully charged via the alternator w/o using batt isolators which is the way I would prefer. If you don't want to manage the charging, then batt isolator/s would be best but would increase cost and complexity. Just a matter of preference.

All grounds should be connected directly together and to engine block.

Not really
If all 4 are being charged by one ALT, all will be charged at the same amount at the same time. The lowest will be charged first until all reach same level, then they will all continue to charge. Problem is anyone which has a problem will pull all down.

With an ACR, the start bats will be fully charged first then charge will shift to house bats

With bat switches make sure they are make before break (most are these days) if they will be switched while the motor is running. If its not make before break then there can be a spike from the ALT and could damage it along with other things

In a perfect world this is true, but in the real world, series resistance will be different from one batt/cable assy to another. Lower series resistance will allow more current to flow and higher resistance will limit current. This will lead to uneven charging and can overcharge the batt with the lower series resistance while not fully charging the other batt. The voltage regulator will limit the charging voltage so the batt with lower resistance doesn't overcharge, but this limits current to the other batt with higher series resistance..

I agree having multiple batteries hard wired together is risky. If one shorts internally, it going to get ugly real quick. Boat batts tend to experience more physical shock than car batts which increases the chance of a plate breaking loose and shorting batt internally. If you're anchored in the cove, connecting batteries together would be fine, but while bashing waves, I'd prefer to isolate the batts.

Nobody has pointed out that battery switches have current ratings. "NORMAL" perkos are in the 375 amp (momentary) range. Dumping 4 batteries thru a single medium duty switch? I hope you mount the switch with 1 screw in a real accessible location cause you're going to be replacing it often.

BlueSea makes some 500A (650 momentary) switches that will easily handle 2 batteries.

Guest makes a diesel grade switch good for 800A momentary.

And battery isolators work well for feeding multiple banks of batteries with a single or double alternator.

I don't see any reason not to treat the "house" deep cycle pair as a single bank. Tie them in parallel, and charge and discharge them together. You can connect them to the battery isolator as if they are a single double sized battery. I hear people advising against this, but i tie my house batteries together on my cruiser like that. I use a 3 bank isolator with 2 alternator inputs. I replaced batteries in 2000, 2008, 2016, and 3 of the 6 this year. I use group 31 "Heavy Duty" batteries, hybrid start/deep cycle. They cost about $140 each and I'm very pleased with 6 to 8 years of trouble-free usage. The key is proper charge/float voltage and keeping them topped up w water.

So, tell ustogether your boat is a single or twins. How many amps your alternators put out. Whether you have (or plan to get) aftermarket 3 stage voltage regulators, what each bank of batteries will provide power to.
Then we can start helping you figure if out.