Blown 20A Fuse on Mercruiser 5.0

[dremison]

While cruising, I lost all engine power and electrical systems simultaneously at around 3800 RPMs.
I figured out it was a fuse nearest to the battery switch (pictured) and it was a 20A fuse, for which I had a replacement on hand, luckily. I had no issues on the 20 min ride back in.
My questions are how common is something like this, what could have caused it, and should I be worried more fuse pops are in my future?
The electrical on the boat is not particularly overloaded - the only non-stock electrical devices are a Garmin GPS and a Fusion head unit/remote unit.
Thanks for your time in advance.

 

[mike_i]

Are all connections clean and tight? What does the fuse power?

 

[alldodge]

Being a Merc that 20A fuse should be behind or at least closer to the helm.

In any case something is starting to pull more current. Could be any of the gauges, or anything else on the motor which comes off the key.

 

[Chris1956]

That should not happen normally, IMO. It points to a serious electrical short.

I expect the situation will get worse, and that fuse or more fuses will blow when you least expect it, or at a dangerous time. Be prepared to toss the hook, when it happens, so you do not drift into some hazards, however, it is much more prudent to find out where the short is and repair it.

 

[dremison]

Got it - that’s my fear. I’ll do some googling, but if you have any suggestions about how to diagnose something like that, I’d appreciate some pointers.

 

[dremison]

Are all connections clean and tight? What does the fuse power?

It looks like everything’s clean and tight - it’s one of the fuses right next to the battery switch and it’s literally just labeled “Fuse”. I think it’s literally a failsafe fuse.

 

[dubs283]

it’s literally just labeled “Fuse”. I think it’s literally a failsafe fuse.

What color wires are connected to the fuse receptacle?

All fuses are failsafe fuses

 

[dremison]

I get that, but they’re usually labeled for a specific device. This one literally just says “fuse” and has red wire connectors. Close up pic attached.

 

[dubs283]

but they’re usually labeled for a specific device.

Yes, usually. Not always, especially with accessories

Engine manufacturers will almost always have the output red wire from a fuse with a purple tracer indicating it is fused main power, usually for the key switch

Both wires appear to be solid red. Looks like the one side goes into a romex style wire casing with a black wire? Hard to tell, pics are a bit grainy. You should check where the ends go specifically, e.g. remove the battery switch and identify which post the lead attaches to and trace the other end to see which component it feeds, may require long test leads and an.ohm meter

What boat/engine manufacturers is this?

 

[alldodge]

Looks to me that the wire was added and maybe after manufacture (don't know). Power to the helm should come from the 10 pin engine harness pin 6 as a Red/Purple.

Look at the 10 pin and see if its corroded or has damage to the pins

 

[Chris1956]

A lot of times the power wire from the battery switch will run the bilge pump. It is connected to the battery switch, so you cannot turn it off, however, 20A is a lot of power for most recreational boat's bilge pumps.

Is the power on when the battery switch is off? That could narrow it down. Is anything not working after replacing the fuse? A 20A short can easily melt wires.

Actually, 20A is a lot of power for all but the PTT system and starting system. If could run a small anchor winch, I suppose. It could also be the main feed to the front fuse box, although, I do see another wire on the battery for that.

Are the contacts for the fuse clean? My '88 MerCruiser had a resettable circuit breaker that ran the slave solenoid, and starter solenoid. I would hope you have that as well. Much faster to reset.

 

[dremison]

Looks to me that the wire was added and maybe after manufacture (don't know). Power to the helm should come from the 10 pin engine harness pin 6 as a Red/Purple.

Look at the 10 pin and see if its corroded or has damage to the pins

I will take a look at that tomorrow for sure. I keep it at the Marina now and need to give it a once over before the weekend. Thank you for the response.

 

[dremison]

A lot of times the power wire from the battery switch will run the bilge pump. It is connected to the battery switch, so you cannot turn it off, however, 20A is a lot of power for most recreational boat's bilge pumps.

Is the power on when the battery switch is off? That could narrow it down. Is anything not working after replacing the fuse? A 20A short can easily melt wires.

Actually, 20A is a lot of power for all but the PTT system and starting system. If could run a small anchor winch, I suppose. It could also be the main feed to the front fuse box, although, I do see another wire on the battery for that.

Are the contacts for the fuse clean? My '88 MerCruiser had a resettable circuit breaker that ran the slave solenoid, and starter solenoid. I would hope you have that as well. Much faster to reset.

I am pretty confident the contacts are clean, but I will double check tomorrow. And the fuses are all individually labeled - one for the bilge, one for the radio, and the unspecified one is for the 20A fuse that blew. It is directly next to the battery switch. Could running the boat on both batteries have fried it? I used the both setting for most of the day due to the #1 battery dying from a radio being left on.
Also, I had no electrical issues after the fuse was replaced for the :30 min ride in. Cruised at 3800 RPM with the radio on, no problem.

 

[dremison]

Yes, usually. Not always, especially with accessories

Engine manufacturers will almost always have the output red wire from a fuse with a purple tracer indicating it is fused main power, usually for the key switch

Both wires appear to be solid red. Looks like the one side goes into a romex style wire casing with a black wire? Hard to tell, pics are a bit grainy. You should check where the ends go specifically, e.g. remove the battery switch and identify which post the lead attaches to and trace the other end to see which component it feeds, may require long test leads and an.ohm meter

What boat/engine manufacturers is this?

It is a 2007 Sea Ray 240 and a Mercruiser 5.0.
What would I be looking for with a volt meter?

 

[dubs283]

Little chance under normal operation with a sound system for the fuse to blow using both batteries. If one battery happens to have one or.more bad cells its possible I guess. Heavy corrosion can cause strange issues as well. Load test each battery individually and static, only way to know.

Check the connections on the battery switch, they've been known to fail ime. Plus you'll see which post the fuse in question is wired to

What would I be looking for with a volt meter?

Use an ohm meter to verify which component the fuse is for