Open Circuit - Potential fire in the port engine

[vb2oc0371]

It's been a rough couple of weeks in my boating life. Two weeks ago, I was almost killed when the throttle stuck on my skiff's Yamaha 25hp sending me into a circle of death and crashing into a duck blind. A few days ago an open circuit caused a small explosion/melt down on my bigger boats Yamaha F150 port side engine.

I'm still tracing down the source of the short. It'll most likely be a corroded contact point, or loose connection somewhere in the line.

Below is the wire that melted after I turned the starboard battery switch to ALL. Instantly, a significant amount of smoke poured out from under the power head which caused a scramble for the fire extinguisher on my part. The wire is part # is 66K-82149-00-00.



A couple questions:

1. What purpose does this wire serve? I'm under the impression that the grounding wire is the one right above the melted wire in the pic.

2. I found that the 10A fuse inline with the ground wire connected to the negative starboard battery terminal had a fair amount of corrosion on the male prongs. Could this cause an open circuit that induced the melt down?

3. Has anyone ever changed this wire out. The mechanic that works at the Yamaha Service Center where I bought the replacement wire said it won't be easy. I haven't started that process yet.

Thanks for any feedback, it's truly appreciated.

[cpostis]

It's been a rough couple of weeks in my boating life. Two weeks ago, I was almost killed when the throttle stuck on my skiff's Yamaha 25hp sending me into a circle of death and crashing into a duck blind. A few days ago an open circuit caused a small explosion/melt down on my bigger boats Yamaha F150 port side engine.

I'm still tracing down the source of the short. It'll most likely be a corroded contact point, or loose connection somewhere in the line.

Below is the wire that melted after I turned the starboard battery switch to ALL. Instantly, a significant amount of smoke poured out from under the power head which caused a scramble for the fire extinguisher on my part. The wire is part # is 66K-82149-00-00.



A couple questions:

1. What purpose does this wire serve? I'm under the impression that the grounding wire is the one right above the melted wire in the pic.

2. I found that the 10A fuse inline with the ground wire connected to the negative starboard battery terminal had a fair amount of corrosion on the male prongs. Could this cause an open circuit that induced the melt down?

3. Has anyone ever changed this wire out. The mechanic that works at the Yamaha Service Center where I bought the replacement wire said it won't be easy. I haven't started that process yet.

Thanks for any feedback, it's truly appreciated.

Strange? Why on earth do you have a fuse on a ground/negative wire. I would think if that fuse blew, or contact was bad, it would prevent a fuse on the positive side from doing it's function of protecting the wiring. Possibly the burnt wire you say melted down was the new path to ground, and because of the insufficient size melted down .
I would review your wiring and make sure all is appropriate.

Looks to me that the part you quoted should not be difficult to replace. Here's the parts diagram.
66K-82149-00-00 YAMAHA WIRE, LEAD 3
Check/clean all your connections including plugs, and grounds.

Others will sound in.

Good luck.

[vb2oc0371]

Strange? Why on earth do you have a fuse on a ground/negative wire. I would think if that fuse blew, or contact was bad, it would prevent a fuse on the positive side from doing it's function of protecting the wiring. Possibly the burnt wire you say melted down was the new path to ground, and because of the insufficient size melted down .
I would review your wiring and make sure all is appropriate.

Looks to me that the part you quoted should not be difficult to replace. Here's the parts diagram.
66K-82149-00-00 YAMAHA WIRE, LEAD 3
Check/clean all your connections including plugs, and grounds.

Others will sound in.

Good luck.

This is the wire that I believe to be the ground wire that's fused and is (was) connected to the negative starboard battery terminal (by the number 6 in the pic below).

I'm learning the wiring, and this may seem like basic stuff, but please let me know if I'm wrong. From the battery, it heads aft into a conduit wrapped cluster that's tucked into the starboard quarter of the boat under the deck. I have not unwrapped that cluster of wires to see where it leads, so that will have to be my next step if I want to trace the problem. Right now, if I connect the negative contacts (seen in picture), to the negative battery terminal, then touch either of the positive black or red cables to the positive starboard battery terminal, sparks fly.

[captn tj]

This is the wire that I believe to be the ground wire that's fused and is (was) connected to the negative starboard battery terminal (by the number 6 in the pic below).

I'm learning the wiring, and this may seem like basic stuff, but please let me know if I'm wrong. From the battery, it heads aft into a conduit wrapped cluster that's tucked into the starboard quarter of the boat under the deck. I have not unwrapped that cluster of wires to see where it leads, so that will have to be my next step if I want to trace the problem. Right now, if I connect the negative contacts (seen in picture), to the negative battery terminal, then touch either of the positive black or red cables to the positive starboard battery terminal, sparks fly.

Hmm interesting I thought (as a general rule) only the positive side is fused.

[fairdeal]

fascinating.
The wires on the outside of your LU are there to connect all the parts which are "underwater" together at the same "potential" as the two anodes.

They are not in any way part of the engines "electrical system" - but are effectively "grounded" to the engine block / negative battery cable.

I believe they are stainless steel - not sure you need to replace it unless it is actually separated into two pieces. It doesn't need to have any "insulation" on it.

Just from the brown wire color, my guess is the inline fuse is part of bilge pump wiring (apparently done incorrectly)

[cpostis]

fascinating.
The wires on the outside of your LU are there to connect all the parts which are "underwater" together at the same "potential" as the two anodes.

They are not in any way part of the engines "electrical system" - but are effectively "grounded" to the engine block / negative battery cable.

I believe they are stainless steel - not sure you need to replace it unless it is actually separated into two pieces. It doesn't need to have any "insulation" on it.

Just from the brown wire color, my guess is the inline fuse is part of bilge pump wiring (apparently done incorrectly)

Good points Fairdeal!

vb2oc0371, does your bilge and/or bait well pumps operate? If fairdeal's point on the wiring color is correct, and they should be as far as marine wiring color code goes, you can now ohm with a meter from your pump(s) and or float/toggle switches to your pump(s) to the fuse connection to confirm if that is what this feeds. You may need a piece of wire to put between the connections to connect your meter leads.

Follow typical bilge/bait well pump diagrams to make sure it is correct.

[greasyshaft]

Assuming that the boat has an aluminium hull....
That bonding wire helps complete the circuit between the bracket unit and the mid section it is not capable of sustaining high current hence the reason the insulation has melted.
I think that something in the boat is shorting to the hull OR some electronic is attempting to use the hull as its connection to the negative battery terminal (via the outboard and through the bonding wire)
Check all your crossover cables between the negative terminals on the batteries, they should be about the same gauge wire as the outboard battery cables

[boscoe99]

Assuming that the boat has an aluminium hull....
That bonding wire helps complete the circuit between the bracket unit and the mid section it is not capable of sustaining high current hence the reason the insulation has melted.
I think that something in the boat is shorting to the hull OR some electronic is attempting to use the hull as its connection to the negative battery terminal (via the outboard and through the bonding wire)
Check all your crossover cables between the negative terminals on the batteries, they should be about the same gauge wire as the outboard battery cables

I got a hundred to one odds that it is.

There is a bad electrical connection somewhere. The bonding leads are trying to serve as power feed leads. Won't work.

[rodbolt17]

fix your ground cable between the battery and the engine.

[fairdeal]

fix your ground cable between the battery and the engine.

on that subject, I saw these photos last year on another forum:

the poster stated it was a 4 stroke Yamaha (F115 or F150 I think) with which he was experiencing electrical difficulties.

He claimed that the ground cable attachment was "tight" and "looked good"

but upon removing it, found these "mating surfaces" of ground cable lug and engine block.

forum image hosting

imgurl

[vb2oc0371]

Issue resolved.
1. Thoroughly wire brushed and scraped all contact points inline with the current path. The battery contacts were definitely in need of cleaning even though it was done less than 6 months ago.
2. Applied dielectric grease to contact points to improve conductivity.
3. Replaced all wing nuts with nylock nuts on the battery terminals. The wing nuts were not staying tight, which compromised conductivity.

So one last comment/question:
Apparently the burnt wire isn't ground wire, but a bonding wire which connects the power head to the lower unit. It's not a current carrying wire. Usually when there's a high resistance in the negative due to it not being connected or loose corroded contacts, current flows via an alternate path using this bonding wire.

Since the bonding wire wasn't melted to the point of separation, I'm curious if can apply a coat of marine grade electrical tape to it instead of replacing it. The Yamaha mechanic said it's not an easy job to change it out, and honestly I haven't gotten up under the engine to judge the level of effort (boat is on lift so it's chore to get up in there).



Thanks.

[pstephens46]

on that subject, I saw these photos last year on another forum:

the poster stated it was a 4 stroke Yamaha (F115 or F150 I think) with which he was experiencing electrical difficulties.

He claimed that the ground cable attachment was "tight" and "looked good"

but upon removing it, found these "mating surfaces" of ground cable lug and engine block.

forum image hosting

imgurl

I bet he figured this out after buying new batts, R/R, batt switch etc....

[fairdeal]

Since the bonding wire wasn't melted to the point of separation, I'm curious if can apply a coat of marine grade electrical tape to it instead of replacing it. The Yamaha mechanic said it's not an easy job to change it out, and honestly I haven't gotten up under the engine to judge the level of effort (boat is on lift so it's chore to get up in there).

You don't need to do anything to it; that plastic covering is purely for aesthetics, not "insulation".

Mercury, for instance, on their version of the F90, used plain SS cable

photo hosting sites

[fairdeal]

Since the bonding wire wasn't melted to the point of separation, I'm curious if can apply a coat of marine grade electrical tape to it instead of replacing it.

Glad to hear you fixed the underlying issue.

You don't need to do anything with that wire, the plastic covering is there for aesthetics, not "insulation"

Mercury, for instance, on their version of the F90, used plain SS cable for those.

photo hosting sites

[99yam40]

Issue resolved.
1. Thoroughly wire brushed and scraped all contact points inline with the current path. The battery contacts were definitely in need of cleaning even though it was done less than 6 months ago.
2. Applied dielectric grease to contact points to improve conductivity.
3. Replaced all wing nuts with nylock nuts on the battery terminals. The wing nuts were not staying tight, which compromised conductivity.

So one last comment/question:
Apparently the burnt wire isn't ground wire, but a bonding wire which connects the power head to the lower unit. It's not a current carrying wire. Usually when there's a high resistance in the negative due to it not being connected or loose corroded contacts, current flows via an alternate path using this bonding wire.

Since the bonding wire wasn't melted to the point of separation, I'm curious if can apply a coat of marine grade electrical tape to it instead of replacing it. The Yamaha mechanic said it's not an easy job to change it out, and honestly I haven't gotten up under the engine to judge the level of effort (boat is on lift so it's chore to get up in there).



Thanks.

My thoughts are that if the bonding wire still has good conductivity (not high resistance) it should be OK.
If it has bad connections due to the overheating then there will be a problem with everything not being protected by the anodes as well as it should