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2007 40HP Mercury 4 stroke

D

Don Fogleman

New member
I have a 40 HP Mercury 4-cycle engine. We were fishing, it started to rain, started the engine to leave. It started normally, though it seemed to idle rough. Accelerated slowly and the alarm sounded, power was drastically reduced, then the engine stopped. Was towed to dock. When we got it home found a 25amp fuse blown on the engine (not fuseblock). Replaced fuse, as soon as ignition switch is engaged; fuse blew again. Also, when the ignition switch is turned on there are 7 beeps. Only had the boat since April and no problems before this incident this morning. Is there something we can do or does this sound like a problem a Merc tech needs to look at?
 
The fuse blows because there is a direct short in the electrical system...it could be anything. You can look at the wiring for melted insulation. Start at the voltage rectifier/regulator bullet connectors...they seem to be a weak and piss poor connection. Let us know what you find.
 
Thank you for responding. the boat is in good repair. There is nothing visibly wrong with the boat or motor. I am attaching a photo showing the fuse placement. The wires connecting the fuse are red and red with yellow stripe. With this infromation, could you point me a direction to look for a short?
If it is not something user repairable I will take it to a qualified service technician. (This is our first boat, therefore, I no nothing about marine engines) Thanks again for your reply.
 
(This is our first boat, therefore, I no nothing about marine engines)
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Without electrical knowledge it is not repairable by you. Take it to a dealer and let a professional repair it.
 
guyjg said:
Without electrical knowledge it is not repairable by you. Take it to a dealer and let a professional repair it.
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I do have some electrical knowledge, just not about marine engines. I know a short causes the fuse to blow; I know which fuse is blown, I know the color code of the wires which the fuse protects. What I don't have is a skematic to know what the wires connect.
Merc40HP.jpg

I apprecciate your time and input. I will take it to a professional, however, I use that term loosely. Far too many times I have gotten professionals to do something with bad results and had to redo it myself to fix the problem.

Thanks again!
 
I know the color code of the wires which the fuse protects.
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In that case start troubleshooting w/your eyes, hands and nose. Buy a manual and box of fuses. Factory manuals are best...$85 from Merc. Do you have an ohmmeter? No? Get a digital volt/ohmmeter for testing. Follow the wires to their termination points. Smell for burned wires or components. Look for arcing points, bare wires touching ground or obvious shorts from corrosion or debris. Save your money until you can't go any further. Isolate components by disconnecting them and try another fuse. Look for a mouse nest...could be under the fly wheel. They like to chew wires.
 
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