So I'm trying to fix the rats nest on this '87 sun tracker, 35hp Merc.

Can anyone explain to me how a boat is typically wired? Starting from the very beginning, there are two heavy gauge wires that feed into the engine cowling, one positive, one negative. I found a fuse in the cowling on the positive side. From there it is housed in a wire harness with all the other ignition controls up to the console. So now in the console that red positive wire is always hot. Should I be using that wire to power running lights, etc.? Or should I run another positive and negative wire to a fused wiring terminal in the console and power it that way so it doesn�t run through whatever electronics are in the motor?

So it basically boils down to this, should all of the regular boat electronics run on the single positive wire coming from the wiring harness, or should I run a separate wire to a fuse panel, and power the running lights, depth finder, etc.?

lights should be on there on circuit and so on .Less problems running down problems later .

The boat I bought had a 2 or 3 owners and the repairs were a mess. I mounted 2 fuse blocks ( 4 each)under the console
easy to
accses .I mounted acommon ground lug .All gauges and such have a fuse to match the load and all black wires are on the same
post.

I found this site helpful.

wiring a boat

Rewiring your boat is a real labor of love, but there's lots worse ways to spend a weekend. For sure keep your accessory wiring separate from the engine wiring harness, and for sure use fuses.

Purple wire coming from the keyswitch usually supplies 12V for accessories (only powered when the switch is "ON"). The only thing I have on there is the tach. Everything else (lights, pumps, horn) is just like sae said - powered through a fuse box wired directly to battery, and common ground bus bar.

Take pictures, lots of them before disconnecting. Can save your butt.

Stay with boating industry standard wire colors for the different systems. The labels and tags will fade or fall off.

Also, use AWG tinned wire and not the SAE stuff from Home Depot or the auto parts stores. Size for size, the SAE wire is 12-18% smaller and will handle less current with more voltage drop. There are wire sizing charts all over the internet. Download one of them. Select your wire size for a 3% drop and when calculating distance of wire runs don't foeget to figure in the length for the return neg wire.