Fried ground wire on Nissan 40 see pic.

oregonducker

Petty Officer 2nd Class
Joined
Feb 10, 2004
Messages
189
2002 Nissan model NS40D2 ser. #50777<br />Yesterday a friend and I were on the river when something odd happened. The boat was beached with the motor off and had been for several minutes. The key was still in the run position, my friend always stops the motor with the kill button instead of turning the key off, old habit from motors with no key. It was also in the down position(prop in the water) when we noticed a really bright light just under the power head. Realized it was a small fire and splashed water on it and then disconnected the battery. There was a strong smell of burned plastic or rubber. Couldn't see anything burned where we saw the light so we took the lid off but couldn't see or feel anything hot or burned in there either. When we left we started it with the pull cord leaving the battery disconnected. It ran like it always does. Once out of the water we reconneced the battery just long enough to get the motor raised and could see the burned wire in the picture. Nothing bad happened while we had the battery reconnected for those few seconds. I'm assuming that it's a grounding cable since it is just bolted to two parts of the motor. There are two more of these wires lower down on the motor. The one in the middle is broken and the lowest one shows blackened and melted insulation but not as bad as the one pictured. Any idea what caused this? Should I have it checked out before I reconnect a battery or just replace/fix these wires and see what happens? <br />
burnedwire.jpg
 

cp

Petty Officer 1st Class
Joined
Feb 1, 2004
Messages
367
Re: Fried ground wire on Nissan 40 see pic.

I don't have a Nissan, hence don't know specifically about them, but I can assure you that those little wires are not intended to be the return path to the battery. All they do is connect the separate parts of the motor/transom mount/leg together electrically so that those parts are all at the same potential to avoid circulating current flow and the resultant corrosion. Was the center one mechanically broken, or electrically burnt/melted in two?<br /><br />Those wires obviously saw much more current than they're intended to carry, which indicates a couple of possibilities: (1) You lost the intended return path to the battery (-) so the little wires were forced to carry that current, or (2) The battery (+) somehow got to the leg/mount/water and current tried to return to the battery through those wires.<br /><br />When you disconnected the battery, did you take off both cables or one; which? Did you notice a loose connection?<br />When you reconnected the battery to tilt the motor, you were out of the water right? Did you try to run the engine with the battery connected at the washdown area/at home? <br /><br />Look for loose connections in the return path i.e. the battery (-) circuit, and short circuits in the battery (+) circuit. And you should replace the burnt wires before too long.
 

oregonducker

Petty Officer 2nd Class
Joined
Feb 10, 2004
Messages
189
Re: Fried ground wire on Nissan 40 see pic.

My friend was standing next to the boat when all this happend and talking to him more it turns out that the aluminum net handle may have come in contact the a battery post while also being in contact with the aluminum boat. That would do it wouldn't it? He's the one that disconnected both the battery cables and he did it in a hurry so isn't sure just how tight they were. The reason the battery terminals were exposed is that the old battery had recently died and I used my big deep cycle as a temporary replacement. It was too big for the original battery box so it was exposed. Won't do that again. The middle wire you asked about was previously broken. I have not run the motor yet with the battery connected. Only the tilt motor. <br /><br />If that net handle was the problem and I replace those burned wires do you think it's safe to try it out or should I have a pro take a look at anything?
 

cp

Petty Officer 1st Class
Joined
Feb 1, 2004
Messages
367
Re: Fried ground wire on Nissan 40 see pic.

An aluminum boat (we don't see very many of those here)! Yep, if your buddy put the aluminum net handle between the (+) battery post and the (unpainted?) aluminum hull, that could very likely result in what happened. (Scenario (2) in my post above.) The high current probably went from the (+) post through the net handle to the aluminum hull, then through those little wires to the engine block, and back to the (-) battery post. The paint on the engine probably kept the current from going directly from the hull to the engine block.<br /><br />Check the net handle. It'll likely have a burnt or melted/arced/splattered spot or two on it if indeed it was the culprit.<br /><br />Get a multimeter (VOM), set to measure resistance. Disconnect both cables at the battery (but have them connected where normal at the ends away from the battery).<br />(1) Measure resistance from the battery end of the black cable to the engine block; you should measure essentially zero resistance (ohms). Make sure the VOM is set to the lowest (x1) scale. If you have those little wires connected, you should also measure close to zero ohms between the battery end of the black cable and the hull. If the little wires are disconnected, you should see a higher resistance, maybe on the order of tens of ohms. If you don't get essentially zero between the black cable and the block, you've got a bad or broken connection in the (-) leg of the circuit. Find and fix it.<br />(2) Next measure from the battery end of the red cable to the block; you should see infinite or very high resistance. With the battery still disconnected, turn the ignition key to the RUN position while noting the meter reading. You should NOT see a zero reading. (Again, I don't have a Nissan, so can't tell you exactly what value you should see because I don't know what may be connected in the RUN position.) Then while reading the meter, turn the key to the START position and hold. You should see the resistance drop significantly as the starter motor solenoid coil is connected, but again should NOT see a zero reading. If you do see a zero reading, you've got a short circuit somewhere; find and fix it.<br /><br />Presuming you see burn marks on the net handle, and do see zero resistance on the black cable, but do NOT see zero on the red cable checks above, then you're most likely good to go. Replace all three little wires, and connect up the battery (maybe use a jumper cable on one leg so you can disconnect it quickly if need), being very observant for anything abnormal (hot wires, burning smell). If everything is normal, turn the key to RUN and again check for anything abnormal. If all's well, start 'er up, and again check for abnormal stuff. If all's still OK, shut 'er down, remove the jumper if used, reconnect normal cable and go have fun with the boat!<br /><br />Just put the battery box cover back on ;) .
 
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