2006 Mainship 34 Twin

[Dougv]

This is my first season with this boat. There are three 8D batteries that are 7 years old, one on port two on starboard. I have had problems starting the port motor (just a click) and would like to replace that battery for now. There are only two battery switches that have an on and off position. It confusing which battery actually starts the port motor since I read the two starboard batteries may actually be in parallel. Unfortunately right now I was only able to secure one new batteries the others are on backorder. I would like to replace the one that would be most effective in resolving my starting issue. Thanks for your help.

 

[Bacchus]

Doug,
Welcome aboard TF. Lots of current / past MS owners here so you are in good company.

My 2008 MS 34 HT is a single but came with 3- 8Ds similarly arranged.
My port batty was thrusters (2) only with their own on-off switches & fuses.
The stbd pair were connected with a 1-2-all-off sw and served as both house & start. I did not like the arrangement and have done some rewiring that included moving start to the thruster batty.

I would strongly suggest doing the necessary tracing to figure out how your battys are wired. You should be able to turn both batty sw off and confirm nothing 12V works. Then turn only port batty on and see what works.
I will guess that w port only you may not have power to your 12V distribution panel, but only a guess.
By removing the fiberglass housing at the engine rm air intake (4-6 screws in ER) you get access to the backside of all the power distribution panels and helps a lot with inspecting & tracing.

[EDIT] Doug... when checking don't forget that in most cases the hi amp starting cables run direct to eng/ starter and only the lo amp side of starting relays run through circuit protection ( breakers / fuses). In order to cut power to an eng starter you may need to pull the batty cable connection. My eng starter was connected to the the main batty selector sw.