complete rewire

[Sangster21]

I am doing a complete re wire on a mercruiser powered 21 footer. The engine is an inline 6 that I am adding the petronix electronic ignition to. The stock wiring harness is toast and I plan to re wire it myself. Does any one know of any links or resources to help me design the system, I do have the factory manual but am interested in professional details to make the job turn out well. I am adding downriggers, vhf, sounder, radar,new guages etc. I know there will be "smart" ways to switch and wire all these components and I would like to get it right the first time. Any help in this regard would be much appreciated.
Regards,
Alan

 

[Silvertip]

Re: complete rewire

It doesn't get any more professional than the diagram in the Mercruiser Service Manual. That by the way, is just one of the two electrical systems on y9ur boat. The accessories you are adding have no interconnection with the "engine electrical system". Those items get connected at a fuse or breaker panel at the helm that is fed by a red and black pair of #10 or #8 of wires that runs directly from the battery. The only thing the engine harness powers is the engine itself and the instruments. If you look at the "stickies" at the top of this forum (not the top of this page) you will find a Generic Boat Wiring Diagram. It applies to most recreational boats.

 

[Sangster21]

Re: complete rewire

I will indeed be following the mercruiser manual for engine wiring. Instead of the factory harness at the main breaker location, I was thinking of using terminal block(s) at the transom to tie the engine to the wiring run to the dash. From the comm terminal on my battery selector switch I believe I should run a short lead to a 50 amp or so breaker to feed the accessories and forward fuse panel/switches. Do most also use a negative bus near the batteries or do you just run all the ground feeds to the battery directly? Looking thru the blue seas catalog can get a bit confusing. I would like to order most of my supplies online and would like to get it all in one shot if possible.
Alan

 

[Silvertip]

Re: complete rewire

Look at the Generic Boat Wiring Diagram in the stickies. Why would you run all of those wires all the way back to the battery? It is a waste of wire. If you are doing a complete rewire, use a fuse panel that has a built-in ground buss (like the one below). All grounds get connected to it. You then run ONE #8 or #10 black wire back to the negative terminal of the battery. And No! -- You use the engine wiring diagram to keep that wiring in it's own harness. That harness is automatically fed from the large red battery cable and it also serves as the charging line from the alternator. There are two electrical systems for a reason. Boat manufacturers don't always know what engine is being installed in their boats but they do know what their boats contain in the form of accessories so they do include the "Boat" wiring. Engine wiring comes with the controller and the engine. Before you even begin this project you are advised to draw a complete wiring diagram. Failure to do so will likely result in a mess worse than you had to start with. And just so you know, there is a difference between a wiring diagram and a schematic.

 

[Sangster21]

Re: complete rewire

Thanks for the replies, I still have some questions as I plan this all out. I still have weeks to go before I need to start wiring. I did not plan to run my accessory grounds back to a bus at stern. I will be adding downriggers for example and they require 30 amp protection for each one so I don't want to run power up and back for that. I was only suggesting a neg bus at transom to create a tidy place to tie in. I have a 12 circuit blue sea fuse panel with ground bus on order as well as a fused 5 circuit switch panel (with power outlet) and a 6 circuit fused switch panel. I will run the 8 guage power to the fuse panel and then I feed the switch panels from a circuit each from the fuse panel.
I have been studying the mercruiser wiring diagram and it seems to me that the feed for the instruments is protected at best by a 40 amp breaker. Should the ign wire feeding the instruments have an in line fuse?
I am trying to get this all figured out by the time I am ready to start wiring. By the way I am starting on a wiring diagram and will post it when it is done to get some feed back please.
Thanks
Alan

 

[Silvertip]

Re: complete rewire

That breaker protects the engine systems as well as the instruments. If you are adding downriggers (as in more than one) you had best do some load calculations so you don't overload the #8 wire feeding the panel.