What are these four terminals?

[Spawnsterdog]

As you can see the wiring on my Oceanis 343 is a real mess and this is after removing two large carrier bags worth other device wiring. I am proposing fitting a busbar for the negative terminal and taking it from there on a voyage of discovery. There are four main terminals. Two red and two black. One of the red ones has nothing coming from it. Does anybody know why there are two of each as the service batteries are wired together. Thanks in advance. (The image is upside down for some reason)

 

[andsarkit]

You really shouldn't have too many ring terminals on one bolt. There is a real possibility of some corrosion in the stack causing problems. The second bolt is to share the connections but as you said, positive and negative busbars with individual connections is the preferred option.
It is possible but unlikely that one of the terminals is permanently live bypassing the main switch for a bilge pump.

 

[pmagowan]

A lot of these things have just been added to by successive owners and have no logic or plan. I suggest start from scratch and have a plan. You can then make sure your batteries are correctly wired, fit a VSR if required, appropriate fuses at battery and a simple and well labelled main panel. There are lots of options for how you do it. Many people use a good bus bar for negative side and a blade fuse positive panel. Sometimes these are combined like this:

 

[Spawnsterdog]

A lot of these things have just been added to by successive owners and have no logic or plan. I suggest start from scratch and have a plan. You can then make sure your batteries are correctly wired, fit a VSR if required, appropriate fuses at battery and a simple and well labelled main panel. There are lots of options for how you do it. Many people use a good bus bar for negative side and a blade fuse positive panel. Sometimes these are combined like this:
View attachment 141238

Yes I have a plan, additional switch panel and busbar, I just wondered why the double terminals?

 

[Major_Clanger]

Yes I have a plan, additional switch panel and busbar, I just wondered why the double terminals?

It might indicate the batteries were once independent of one another.

 

[Refueler]

I am in process of drawing up my own Switch Panel and then 3D print it. I think like many others - the on-shelf offerings are compromises ....

Pal of mine removed a very nice panel from his B31 - but again it was not quite what he wanted ... being Commercial Mgr of a Metals factory - he had his own design made up ... added switches / breakers / displays etc.
Its a work of art !
It triggered my action to try do same ...

 

[ChromeDome]

Bus bars (pos and neg) is the core of proper and safe wiring.

I had three Vetus switch panels (switch / glass fuse / LED when on) beginning to fail on the LED's. Thus commonly having something turned on without me noticing when leaving the boat in the evening.

New panels of any acceptable quality are expensive beyond justification - even worse if looking for backlit and eye watering if wanting integrated circuit breakers.

In my case the solution was to replace the panels with water proof membrane touch panels. More switches, all relay controlled, circuit breakers, backlit and tidy.

Cleaned up a lot of wiring and, more importantly, took the opportunity to mark up all wires with printable labels.

Before:




After:

 

[Stemar]

I took a different approach - I fed my supply - fused near the battery to a couple of these, via a master switch, then on to individual switches as needed. A bus bar for the negatives and cable ties to keep everything neat.

The LEDs light up if the circuit is live but the fuse is blown, which makes it easier to find a blown fuse in poor light, though the only time I've ever had fuses blow was through my own stupidity

 

[LadyInBed]

I see that your main neg and 2x pos terminals are screwed directly into the wood. I would advise mounting them on an insulating plate as although wood isn't a good conductor, if the wood gets any damp in it you will get some leakage current.