Wiring Harness Meltdown

[CTW24]

I have a 2003 Mercury 25 2 stroke that has a serious wiring harness issue. The black ground wire melted from the inside the motor all the way through the wiring harness into the control box. What could have caused this? I have 2 batteries wired through a main switch as pictured. Any help would be appreciated.

 

[Yegboats]

Reverse polarity

 

[CTW24]

Reverse polarity

Can you explain what this means. Looks like I have to replace 2 wiring harness and I dont want to repeat this mistake. Thanks

 

[CTW24]

Can you explain what this means. Looks like I have to replace 2 wiring harness and I dont want to repeat this mistake. Thanks

When I replace the internal and external wiring harness what am I looking for to avoid another meltdown?

 

[merc850]

Did you have both charging systems feeding the battery(s) at the same time?
that could have caused it. Usually on a dual install with 1 battery you have 1 motor's charging system disabled. Where does that wire come from?

 

[CTW24]

Did you have both charging systems feeding the battery(s) at the same time?
that could have caused it. Usually on a dual install with 1 battery you have 1 motor's charging system disabled. Where does that wire come from?

I only have 1 motor 2 batteries. The wire comes from the rectifier and runs to the kill switch on the shifter controls. It's a black wire which would indicate a ground wire.



n it's a ground

 

[CTW24]

I only have 1 motor 2 batteries. The wire comes from the rectifier and runs to the kill switch on the shifter controls. It's a black wire which would indicate a ground wire.



n it's a ground

Maybe to much resistance on the main power cables running to the battery? I have 2 GA cables. Or a loose connection? Is there a way to test resistance with a multimeter?

 

[CTW24]

Maybe to much resistance on the main power cables running to the battery? I have 2 GA cables. Or a loose connection? Is there a way to test resistance with a multimeter?

Can a rectifier overvolt the charging system and produce the kind of damage seen in the pictures? Is there a way to check the voltage produced by the rectifer?

 

[Roadking57]

Yes you can read resistance as ohms with a voltmeter. First you must isolate the circuit you are testing to get a true reading. The only way I know to check voltage output from a regulator is at the battery terminals with a voltmeter. Take a reading of battery voltage in off mode, start engine and take another reading, and one reading above idle.

 

[Scott Danforth]

The black ground wire melted from the inside the motor all the way through the wiring harness into the control box. What could have caused this?

something shorted or that ground wire that ran to the controls for some reason received a larger load on it than it was designed for.

did you add any accessories to the boat?