15a fuse blows immediately on mercury 60

[Alanwray]

I have a 60 mercury and the 15a fuse blows intermittently. I have disconnected all instruments at dash and still fuse blows. Seems to me something is wrong at the motor. I’ve checked the diode at the motor. Also don't see any corrosion at any connections. Has anyone seen this issue or know what is the next thing to check.

 

[Willyclay]

Welcome to the forum. The members are great and should be able to help you with your problem. It would help them if you posted the model number of your motor. I personally chased a "ghost" like you are describing on my old Johnson. My problem was invisible corrosion inside the wires at the inline fuse connector. Good luck!

 

[Texasmark]

Welcome to the forum. The members are great and should be able to help you with your problem. It would help them if you posted the model number of your motor. I personally chased a "ghost" like you are describing on my old Johnson. My problem was invisible corrosion inside the wires at the inline fuse connector. Good luck!

Good point here.

A corroded fuse to connection interface becomes a resistive element. Pushing current through a resistance generates heat and heat from over current conditions is what blows fuses. If the heat is coming from the fuse to terminal connection it has no way of knowing what is producing the heat that makes it blow.

 

[Texasmark]

Other than mentioned above, follow the lead leaving the fuse and find connections attached to that point. Remove all but one and start with that connection. If the fuse holds, start adding wires one at a time and testing. Your problem circuit will raise its head. Then we will help you troubleshoot that circuit.

 

[Willyclay]

Is there any chance that your fuse should be rated at 20A? Mine was and the owners manual for a 2004 Mercury 3-cylinder 60HP motor also lists that fuse as 20A. You need to be certain of the specs before proceeding. Good luck!

 

[pollard]

It sounds like you’ve already done a thorough check. Given that the 15a fuse blows intermittently despite disconnecting and copy all dash instruments and checking the diode, the issue might be within the motor itself.

Next steps:

• Inspect Wiring: Look for any signs of wear or damage in the wiring leading to the motor.
• Check Ground Connections: Ensure all ground connections are secure and free of corrosion.
• Test Motor Components: Check for short circuits or faults in the motor components.

 

[Willyclay]

I'm hoping he got it fixed and was too busy catching fish or having QFT with his kids and/or grands to let us know what he found over 18 months ago!