Burnt mounting bracket to lower end ground cable

aeviaanah

Petty Officer 3rd Class
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Oct 4, 2011
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A few weeks ago my starting battery rubbed against the side of the bench seats in my aluminum boat causing it to arc out. My new 15hp Mercury 4 stroke (electric start) was hooked up and the only apparent damage was the ground cable that is connected between motor mounting bracket and lower unit. I replaced the cable and terminals and tested motor, seemed to be running fine. Took it out on the water and everything worked great. A few days later i noticed the the cable i had replaced was still intact but looked like it had been hot. I replaced it again just to be sure and it before I even had a chance to get it on the water it had burnt to a crisp, motor was never started.

I did a few tests today and I may be looking at replacing the battery cable. Im thinking when battery arc'd out, It may have heated the cable and ruined it. All connections are clean and had a good fit. Again, this is a brand new motor.

I read this website showing how to test battery cable http://www.ehow.com/how_5455908_check-resistance-battery-cables.html

The positive test- i hooked digital multimeters red wire to positive terminal on battery, i then hooked multimeters black wire to starters positive connection. After holding down starter button Multimeter read .4 V

The negative test- i hooked multimeters red wire to metal housing of starter and hooked black wire to the negative terminal. After holding down starter button Multimeter read .3

The website says anything above .3 is not good. Does it sound like I diagnosed this properly? The motor is still under warranty but since it was my fault I doubt I can get it fixed under warranty.
 

99yam40

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Re: Burnt mounting bracket to lower end ground cable

Sounds like you are taking a voltage drop test of the battery cables, and I do not think that a slightly high resistance in the battery cables would cause current to flow through the bonding jumper on lower unit.
especially if you do not even have to hit the starter to fry the bonding jumper, Something is running current through the bonding jumper to get back to battery.
Maybe you broke the negative wire going to other 12 stuff on the boat and it has to travel through the boat and bonding jumper to get to the neg battery cable attached to power head to return to battery
 

aeviaanah

Petty Officer 3rd Class
Joined
Oct 4, 2011
Messages
77
Re: Burnt mounting bracket to lower end ground cable

Sounds like you are taking a voltage drop test of the battery cables, and I do not think that a slightly high resistance in the battery cables would cause current to flow through the bonding jumper on lower unit.
especially if you do not even have to hit the starter to fry the bonding jumper, Something is running current through the bonding jumper to get back to battery.
Maybe you broke the negative wire going to other 12 stuff on the boat and it has to travel through the boat and bonding jumper to get to the neg battery cable attached to power head to return to battery

All 12v accessories are connected to proper terminals and arent broken in anywhere. Thanks for the help....any other ideas?
 

99yam40

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Re: Burnt mounting bracket to lower end ground cable

Might try to disconnect things and then hook them back up one by one to see what is putting current through it.
A clamp on DC amp meter would help show what is flowing through bonding jumper and when.

You did say the last time you did not even start the motor. So does that mean you did not even turn motor over with the electric start, but the jumper overheated?
 

aeviaanah

Petty Officer 3rd Class
Joined
Oct 4, 2011
Messages
77
Re: Burnt mounting bracket to lower end ground cable

Might try to disconnect things and then hook them back up one by one to see what is putting current through it.
A clamp on DC amp meter would help show what is flowing through bonding jumper and when.

You did say the last time you did not even start the motor. So does that mean you did not even turn motor over with the electric start, but the jumper overheated?

I appreciate you sticking with me to help figure this out. I tested for current traveling through jumper (black on one end and red on the other) using my multimeter on the A~ setting. I had black wire to COM and red wire to 10A. I singled out every accessory and nothing gave an amperage reading. Either I didnt have it set up right or there was no amperage traveling through jumper. Any other ideas?

Is it possible the starting battery is damaged due to arcing out? May it be the problem?
 

ENSIGN

Lieutenant Junior Grade
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Jun 21, 2009
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1,179
Re: Burnt mounting bracket to lower end ground cable

Since the motor is grounded to the boat through the transom bolts or clamping screws there's a good possibity of a short in the motor harness.The first thing to do is BUY A BATTERY BOX AND HOLD DOWN.
 

99yam40

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Re: Burnt mounting bracket to lower end ground cable

I appreciate you sticking with me to help figure this out. I tested for current traveling through jumper (black on one end and red on the other) using my multimeter on the A~ setting. I had black wire to COM and red wire to 10A. I singled out every accessory and nothing gave an amperage reading. Either I didnt have it set up right or there was no amperage traveling through jumper. Any other ideas?

Is it possible the starting battery is damaged due to arcing out? May it be the problem?
Battery will not cause current flow through jumper.
Something is causing current to flow where it is not suppose to.

Try disconnecting jumper and then measure across where it normally hooks up in the amp setting to see if there is some current flow
 

aeviaanah

Petty Officer 3rd Class
Joined
Oct 4, 2011
Messages
77
Re: Burnt mounting bracket to lower end ground cable

Since the motor is grounded to the boat through the transom bolts or clamping screws there's a good possibity of a short in the motor harness.The first thing to do is BUY A BATTERY BOX AND HOLD DOWN.
Got one :)
Battery will not cause current flow through jumper.
Something is causing current to flow where it is not suppose to.

Try disconnecting jumper and then measure across where it normally hooks up in the amp setting to see if there is some current flow
I thought this is what I tried to do. Did I do it wrong?
 

99yam40

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Messages
9,116
Re: Burnt mounting bracket to lower end ground cable

Did you disconnect the jumper or get in series or did you just parallel it
 
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