Engine Cuts on Load Blows 15A Fuse

[NickT]

Hi,

Several months ago, after running the boat off and on for more than 45 mins, the engine cut off abruptly while on the move, and ignition dead thereafter. I discovered blown 15A (ignition) fuse (under dash). Hardwired and limped home.

Mechanic was unable to replicate the issue, replaced it with a 30A fuse, to which I was very uncomfortable. I switched it back to 15A and all was good till last month. While trouble shooting, I discovered leak (at the HT contact point) in the ignition coil and replaced it. Problem (under same conditions) persisted until fuse was replaced with a20A. However, engine did cut a couple times but did not blow that fuse.

While running the boat and trouble shooting, I discovered some weakness in the + wire going to the ignition coil. The internal break near the lug fixed and it worked well (20A fuse), so I downgraded it to a 15A. Engine started much easier than before, and yesterday was a great day out at sea until the fuse blew, about 3 hours into our outing! Replaced with a 20A and headed back at cruising speed without any issues.

Has anyone encountered the same issue?

Is is OK to replace the 15A to a 20A fuse?

While doing visual trouble shooting, the radio cut off whenever the main lead to the battery was moved, removed the main Power (rotary knob that connects to the battery) Switch and discovered a crack thus contact was a little loose to the switch mechanism. It broke off when I was fiddling with the contacts.

Not sure if this has anything to do with the issue that I am facing.

Side note, the ignition alarm for starting / cranking stopped working about a year ago, but sounds off on high temperature.

Appreciate your comments and help!

Nick Tay
2006 Maxum 2100SC Mercruiser Alpha 5.0 Carb.
2nd owner, since 2009

[mmwjr]

Welcome aboard

From what I recall the ignition fuse is 20 amp. So you have owned this boat for 9 years and never replace this fuse befor and it was 15 amp? Did you change anything recently, add any electronics and powered it off a helm gauge?

Regarding the alarm not self testing at start up it may be the oil pressure switch is bad. The switch is closed when there is no oil pressure and completes the alarm circuit, once started the switch opens.

[Gugi47]

Welcome aboard
Like Mike say in his post. You should have 20A or 30A fuse.
Is very common to have a loose wire. Most of the time the positive (+) can do that.
I would go and tighten all the wire connection. Special the one from starter and alternator. Replace the faulty selector switch.
The other thing can be, a broken wire terminal (+) what sometimes make connection the the ground (-) and blow your fuse. That should be in the engine compartment.
Good luck with your search.

[NickT]

Originally Posted by mmwjr

Welcome aboard

From what I recall the ignition fuse is 20 amp. So you have owned this boat for 9 years and never replace this fuse befor and it was 15 amp? Did you change anything recently, add any electronics and powered it off a helm gauge?

Regarding the alarm not self testing at start up it may be the oil pressure switch is bad. The switch is closed when there is no oil pressure and completes the alarm circuit, once started the switch opens.

Thanks!

According to the schematic drawing in the Maxum owners manual, it is 15A. (Please see attached).

Didn’t add anything new.

Will source and replace the oil pressure switch.

[NickT]

Originally Posted by Gugi47

Welcome aboard
Like Mike say in his post. You should have 20A or 30A fuse.
Is very common to have a loose wire. Most of the time the positive (+) can do that.
I would go and tighten all the wire connection. Special the one from starter and alternator. Replace the faulty selector switch.
The other thing can be, a broken wire terminal (+) what sometimes make connection the the ground (-) and blow your fuse. That should be in the engine compartment.
Good luck with your search.

Thanks for your advice! I will run through all the connectors.

[mmwjr]

Originally Posted by NickT

Thanks!

According to the schematic drawing in the Maxum owners manual, it is 15A. (Please see attached).

Didn’t add anything new.

Will source and replace the oil pressure switch.

Interesting as the Maxum wiring diagram for my boat also shows a 15 amp fuse however the Mercruiser diagrams I looked at show 20 amp.

[NickT]

Originally Posted by mmwjr

Interesting as the Maxum wiring diagram for my boat also shows a 15 amp fuse however the Mercruiser diagrams I looked at show 20 amp.

Hi,

Isn't the 20A in Mercruiser diagrams referring to the one on the engine block?

What do you, and others with a similar Maxum boat / engine, have is the fuse block underneath the helm?

Thanks in advance!

[mmwjr]

Originally Posted by NickT

Hi,

Isn't the 20A in Mercruiser diagrams referring to the one on the engine block?

What do you, and others with a similar Maxum boat / engine, have is the fuse block underneath the helm?

Thanks in advance!

To be honest I never looked to see what size is in the fuse block.

There is a 90 amp fuse on the starter and a 50 amp breaker on the engine. The Mercruiser diagram shows the 20 amp fuse at the helm.

[NickT]

Originally Posted by mmwjr

To be honest I never looked to see what size is in the fuse block.

There is a 90 amp fuse on the starter and a 50 amp breaker on the engine. The Mercruiser diagram shows the 20 amp fuse at the helm.

Hi Mike,

Thanks for sharing, I'll keep to the 20A.

Hope the engine doesn't cut again.

Thanks!

[mmwjr]

Originally Posted by NickT

Hi Mike,

Thanks for sharing, I'll keep to the 20A.

Hope the engine doesn't cut again.

Thanks!

Just don’t go any larger than that as the wiring is not rather for higher current. If it lasts to the end of the season you may want to investigate more size the 15 amp lasted 12 years with no issue something has changed.

[mmwjr]

Get an inductive amp meter to put around the wire to see how much current is being drawn.