Almost burned the boat!

[Scubacruiser]

1994 Campion with a Volvo Penta 4.3 GL

Went to hook up the battery for a first start after winter storage. There were no signs of any rodent activity. I hooked up the positive and wrenched the nut on the terminal. Then I hooked up the negative and noticed a fairly large spark. It seemed fine so I started doing up the nut. The nut got hot and smoke started coming out. The nut was too hot to touch! I had to run for a glove and a fire extinguisher. I sprayed the area and then managed to get the nut off and pull the cable.

After the yellow dust settled from the extinguisher, I started checking where the burning wire smell was coming from. Under the dash there was no smoke and no warm wires. Under the engine cover everything seemed fine. Nothing hot. Alternator was cool. Starter cool.
I found a twisted cable under the left rear of the engine that had corroded through. It appears to connect to a ground lug at the right rear of the engine, then goes to the lower center of the transom. The insulation on the wire is brittle and burnt but it was not warm. It just flakes off. Since it's a ground wire, how could it have caused smoking? Is it for grounding the outdrive?

 

[alldodge]

Was it only one battery and one set of cables?
Cables get hot because of current draw, something is pulling current.

 

[sam am I]

So I have to ask, did you hook up the battery backwards? Perhaps the battery was not fully/charged enough to immediately throw off molten metal but, was low on charge (or weak/aged) and yet still charged enough to give a good "fairly large" spark when first attached the cable, then it possibly proceeded (10,20,30 sec'ish) to heat your nuts

and melt wires..........

Can you still go look at it and perhaps do some forensic work and see if you might have?

BTW, glad no one got hurt and good call on having the fire extinguisher handy...

 

[thetmaxx]

Corroded ground wire doesn't sound suspect, I would also wonder if the cables got connected backward. I've done it, and the cables get hot quick. Then you have to find out what is burned up....
Another
If your sure you connected it correctly, you could use a test light between the positive cable and positive battery terminal (negative terminal connected) and try disconnecting things until it goes out, like starter, alternator, ignition, etc. You might not necessarily be able to feel the problem item get hot if it was shorted.

 

[Scubacruiser]

Cables were definitely connected properly. The only thing that has changed since last year was a new ignition keyswitch. But I replaced the old with the same type and connected the wires one by one verifying they were correct. I will of course recheck it before I do anything else. Key was off when hooking up the battery.

 

[Scubacruiser]

No Title

Here is the twisted cable that is corroded and burnt. Is this the outdrive ground strap?

 

[Scubacruiser]

One battery - just came off the charger. It was new last summer and stored with a maintainer in my basement over the winter.

 

[alldodge]

The wire does look like the engine block to transom assembly ground connection, but it also looks like it has gotten hot and one time.

With only bat cables being connected, there has to be an issue with on of them. What I don't get right now is how was there smoke coming from under the helm, yet nothing was burnt

 

[Scubacruiser]

The smoke was coming from the engine area. No smoke coming from under the dash.

 

[alldodge]

The smoke was coming from the engine area. No smoke coming from under the dash.

OK, my bad

Sure is puzzling. Did you happen to adjust the alternator or starter wires, or replace any of those last winter?

 

[Scubacruiser]

Last season I had troubles starting it where a key wiggle would allow the starter to work. No other problems. Ran it to do winterization, then removed battery and parked it until this past weekend. I installed the new keyswitch first (which I will check again), then the battery. And I did not notice any rodent activity. My alternator was checked at the start of last season and found to be good.

 

[alldodge]

I'm pretty much out of ideas, it's pretty simple connections. If you have an ohm meter, check the positive cable to ground, it should read hi

 

[thetmaxx]

That cable sure does look cooked. Very likely the source. was it possibly laying on the starter power terminal?

 

[Scubacruiser]

Yeah, the insulation on the cable just flakes off. I've never seen a ground strap made up of 3 twisted wires like that.

I don't think it was touching the starter terminals. The cable wasn't long enough to make contact.

I haven't had a chance to do anything on this all week as it has been raining every evening. It's supposed to rain all weekend too, but I hope to spend some time checking things over between raindrops.

 

[alldodge]

I had one of those burn up on me after installing a motor. A guy helping me was hooking up the battery cables and forgot to tighten up the main negative on the block. The connection between the transom assembly and the battery had a better connection then the main cable. So as soon as we tried to start the motor most the current went thru the small wire instead the cable. One of those :facepalm: moments

The difference is you have the issue when first connected which shouldn't happen

 

[Scubacruiser]

I managed to do a bit more investigating. The harness from the fuel level sending unit on top of the tank to the transom is completely melted. The insulation and conduit is melted to the carpet. I'm lucky the fuel tank didn't ignite! Included in the harness is the wiring for the bilge pump as well. Though those wires seem to only have melted due to their proximity to the fuel level wires.

I'm going to replace the fuel sender.. Plus all the wiring related to this issue. Everything else seemed fine, including the new ignition switch.

 

[sam am I]

Weird, the things you described should all have fuses........and normally the fuel sender wire (the power feed wire) that runs from the gauge to the tank into the sender is current limited

The meaning of that is.......Due to internal resistance inherent to a/the fuel gauge's design, you could have, at any point along this wire, taken your pocket knife and pealed back the insulation and touched that point to ground and the only thing that would have happened would be the fuel gauge needle would have pegged. i.e., Shorting that wire to ground anywhere in its path to the tank can't hurt a thing....

So unless something failed internal to the gauge, which is possible, very remote thou but, my gut says the sender or the gauge aren't the cause, just the effect sounds. Also if the gauge failed to limit current on this wire that became grounded somehow, the fuse would have popped at that level of current to melt things.

You said "bilge pump wire" ran in the loom? but I know Its hard to tell sometimes thou.............it's an ULGY melted mangled mess, however......... perhaps this bilge pump had a "direct to battery" un-fused wire? Maybe someone/PO did some re-wiring in the boat at some point prior to you owning it?

***side notes***

Think some of us can admit to having something like this happen at some point in our lives, car, boat, bread board project, whatever BUT, the one thing that so sticks in your head, and of course this is if you knowingly do something dumb, like not properly fusing something to save time or money, is......"a simple $0.10 fuse would have prevented an entire melt down"

I'm hoping this isn't your case thou and it was totally un-preventable but, most (99.9%) are preventable with proper fusing and those people won't ever have this happen to them the stats say.

I just hope a PO didn't compromise you or anyone else safety .....If this would have went down out on the water with no where to go but in the drink.....Not trying to be a scare monger but, there is no other feeling like that, been there done that!!

 

[Scubacruiser]

I replaced all the burnt wiring this weekend. I then checked for current draw and found just over 4A with everything turned off. I'm pretty sure the bilge pump is the culprit. I had to pull the cover back over due to rain and other commitments, so I'll have to pull the pump this week.

 

[H20Rat]

I replaced all the burnt wiring this weekend. I then checked for current draw and found just over 4A with everything turned off. I'm pretty sure the bilge pump is the culprit. I had to pull the cover back over due to rain and other commitments, so I'll have to pull the pump this week.

How long did you leave the multimeter on? Depending on your electronics, various things can draw power for a couple seconds to a minute or more while they are recharging internal capacitors and batteries. (engine EFI systems, radios, depth finders, etc...)

In any case, leave your multimeter attached and start pulling fuses.

 

[Scubacruiser]

There isn't much electronics on my boat. No EFI. I have lights, pump, blower, horn, stereo and fishfinder. The fishfinder is not in the boat at the moment. I did in fact leave the meter attached for some time.

I also don't have fuses for all circuits. Some have push to reset breakers. I'll have to individually pull the wires to tell.