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  1. 03-13-2019, 02:57 PM #1
    fisherman34
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    2000 mercury 200hp EFI melted wires

    Hi, I have a year 2000, 200 hp efi 0T067669 that has some melted wires after the plug coming from ECU. It is the wiring harness after the screw lock plug to ECU and the colors melted are Yellow with Red stripe, Gray with White stripe, solid Green and solid Purple wires. Any ideas on what would cause this? Before i found these wires, it had been running weird. It would start right up and run then it wouldn't restart again for 1hr or 2. Not sure if these wires are the cause or if something else made these wires get hot.
    Thanks
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  2. buster502
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    #2 03-13-2019, 06:52 PM
    has it been charging good
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  3. fisherman34
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    #3 03-13-2019, 07:04 PM
    As far as i know it is charging. My cranking battery is always charged and the volts reading on the electronics is usually above 12v.
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  4. JOE54
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    #4 03-13-2019, 07:09 PM
    if its wires going into ecu I bet It does run weird sounds like short in ecu to me
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  5. kls2020
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    #5 03-13-2019, 10:10 PM
    Yellow / red stripe - enrichment from key "Start"
    Gray white - Knock sensor
    solid green - #1 spark coil
    purple - battery pos. from key switch "ON"

    if melted close to the plug could be a bad connection or connector pin to pin short . What do the pins look like?
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  6. fisherman34
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    #6 03-14-2019, 02:30 PM
    Quote Originally Posted by kls2020 View Post
    Yellow / red stripe - enrichment from key "Start"
    Gray white - Knock sensor
    solid green - #1 spark coil
    purple - battery pos. from key switch "ON"

    if melted close to the plug could be a bad connection or connector pin to pin short . What do the pins look like?
    The pins look good. All of them are clean.
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  7. EuropeanAM
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    #7 03-14-2019, 02:34 PM
    I would send that ECU off for testing, and plan to source a replacement harness to address the ECU connector. Have had a couple do this over the years- only one of them was actually an ECU problem.

    Other two were problems inside the intake manifold (shorting wires).


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  8. fisherman34
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    #8 03-14-2019, 02:35 PM
    Quote Originally Posted by JOE54 View Post
    if its wires going into ecu I bet It does run weird sounds like short in ecu to me
    The wires are going to the ECU. I am thinking i just need to have this ECU repaired. From all the research i have done so far it sounds like rebuilding the ECU is a good place to start.
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  9. fisherman34
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    #9 03-14-2019, 02:41 PM
    Quote Originally Posted by EuropeanAM View Post
    I would send that ECU off for testing, and plan to source a replacement harness to address the ECU connector. Have had a couple do this over the years- only one of them was actually an ECU problem.

    Other two were problems inside the intake manifold (shorting wires).
    Does Mercury still sell wire harnesses for the EFI ?
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  10. EuropeanAM
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    #10 03-14-2019, 02:41 PM
    See if you can open up the wiring near that plug and get a couple good pictures of the wiring and the HARNESS side of the connector.

    Interested in seeing what this one looks like, given the colors mentioned.


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  11. fisherman34
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    #11 03-14-2019, 02:50 PM
    20190313_154722.jpg
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  12. EuropeanAM
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    #12 03-15-2019, 09:18 AM



    From that picture, I would say its very likely that you have had a VARMIT inside your engine cowling. Appears that several of those wires were used as dental-floss.


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  13. fisherman34
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    #13 03-15-2019, 08:39 PM
    Quote Originally Posted by EuropeanAM View Post



    From that picture, I would say its very likely that you have had a VARMIT inside your engine cowling. Appears that several of those wires were used as dental-floss.
    I know it looks as if something chewed on it but i can assure you it is melted . There is a little bit of green melted on to the orange ,gray and yellow wires.
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  14. buster502
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    #14 03-16-2019, 07:27 AM
    my old eyes are going bad,all i see is melted wires
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  15. EuropeanAM
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    #15 03-18-2019, 05:15 PM
    The green one may be partially melted. That wouldn't explain some of the others... of course repair steps would be the same (except that if the wires were chafed by an EXTERNAL force, melting could occur with any wire that carries voltage and came into contact with a ground.


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  16. fisherman34
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    #16 03-21-2019, 05:26 PM
    Could these wires be fixed with liquid electrical tape or should i look for a new wiring harness? After talking to Simon Performance Technology, he thinks this was caused by the ECU so i sent it in for repair.
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  17. EuropeanAM
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    #17 03-21-2019, 07:43 PM
    I would not be inclined to try any "patching" in this area.


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  18. blackboat
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    #18 03-23-2019, 08:04 AM
    It looks to me that the heat source was OUTSIDE of the harness...like a bracket,etc,shorted to a positive and got hot and melted things.Then again,the green wire looks like it was hot and it appears the gray and purple are fused together. Just thinking out loud. On the harness repair,in the car restoration game,that would be one of the easier ones but there has to be some used harnesses out there. Good luck and keep us posted.
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  19. fisherman34
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    #19 03-28-2019, 04:40 AM
    Quote Originally Posted by blackboat View Post
    It looks to me that the heat source was OUTSIDE of the harness...like a bracket,etc,shorted to a positive and got hot and melted things.Then again,the green wire looks like it was hot and it appears the gray and purple are fused together. Just thinking out loud. On the harness repair,in the car restoration game,that would be one of the easier ones but there has to be some used harnesses out there. Good luck and keep us posted.
    Just ordered a new harness. Thought that would be better than a patch job. Does anyone know what the responsibilities are for each color of wire that are melted? Thanks in advance
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  20. silverbullet02
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    #20 03-28-2019, 08:12 AM
    If you don’t have a manual you can just google search and find some diagrams online that have all the wires labeled.
    1995 Allison XB-2003 225 Super Mag. It's slow and I'm ok with that.
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