Fuse blows when engine starts

[TurtleTamer]

I finally read part of the thread you linked in your original post and something caught my eye. That OP posted that he tested one of his ignition wires with his test light and started the boat, which of course should never happen. I'm also still struggling with the fact that your boat started on its own, and then further, it wouldn't run with both battery terminals disconnected (if ground/neg was tied both to engine block and battery for loads).

Without a wiring diagram for that boat, my mind is finding it impossible to look for obvious faults, just the thought that Tahoe has done something funny with the wiring for that year/engine and/or used some kind of faulty component in the starting system that fails closed/shorted. Maybe it's as simple as the start switch itself. Temporarily wire in a pushbutton switch to the slave solenoid (while unwiring the start circuit to the ignition switch) and then unwiring your acc power to the ignition switch while jumping 12v to your acc wire might rule that out. Maybe someone else has a simpler method.

But then, why would the starter be giving you issues now and why would the boat not run once started, with the battery disconnected? That's why I originally thought something may be awry with the alternator. That hidden 15a fuse makes me wonder what was going on with Mercruiser or Tahoe that year range.

 

[apallo1]

I finally read part of the thread you linked in your original post and something caught my eye. That OP posted that he tested one of his ignition wires with his test light and started the boat, which of course should never happen. I'm also still struggling with the fact that your boat started on its own, and then further, it wouldn't run with both battery terminals disconnected (if ground/neg was tied both to engine block and battery for loads).

The belief now, after finding that the 10-pin adapator to go from old school 10-pin to new school had water in it, is that the water caused the short that started the boat. So that’s one mystery solved.

I also couldn’t get over this idea that it worked fine before I had the carb rebuilt, so I kept gravitating back to it. Turns out, there was a wire pinched which was causing the fuse to blow. It also blew the oil pressure sensor which was shutting off the fuel pump and why it wouldn’t stay running.

So now that the boat boat is running, we put it in the water to troll around and do some testing. After about 15 minutes we decide to throttle up and see how she does. Boat won’t come out of the water but engine sounds fine. I turn around and water is pouring in from the engine compartment (yes the plug was in). So we high tail it back to the dock. I’m hoping maybe just a hose popped lose. Soooo I’ve traded 1 set of problems for another...

 

[apallo1]

Expansion plug had popped out. Put in a replacement. Everything seems to work now. Hopefully that’s the last of it. (Knock on wood)

 

[apallo1]

Well.... plug replaced, full throttle, boat won’t cone out of the water. Trolls at 20mph with big wake..... I’m at a loss. I sure hope someone has an idea......

 

[TurtleTamer]

If you popped out a core plug you have have a cracked block/head(s) and/or damaged head gasket(s). I'd do a compression check at this point. No evidence of water in oil? No other external leaks?