electrical issue
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default electrical issue

    I have wired up the autronic ECU and the car runs.

    There is one issue that is way above my understanding of such things, and was hoping someone might point me in the right direction to sorting it.
    I'd like to attempt to analyse it before I give up and take it to my sparky.


    The issue is with the tacho on my dash, and the alt light.
    When the alt light goes off, the tacho goes off too and zero's where it wont budge from until the alt light comes on again.

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    I wouldn't know where to start on this issue, so any advice would be of some help.


    Jo

  2. #2
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jo proffi View Post
    I have wired up the autronic ECU and the car runs.

    There is one issue that is way above my understanding of such things, and was hoping someone might point me in the right direction to sorting it.
    I'd like to attempt to analyse it before I give up and take it to my sparky.


    The issue is with the tacho on my dash, and the alt light.
    When the alt light goes off, the tacho goes off too and zero's where it wont budge from until the alt light comes on again.


    I wouldn't know where to start on this issue, so any advice would be of some help.


    Jo
    1) Disconnect the alternator light at the alternator and check if the problem goes away.

    2) Disconnect the ECU feed to the tacho and see if the problem goes away.

    After isolating what is causing the issue you can start investigating why.

    I would start with item 2 fault finding.

    Are the tacho and alternator supplied 12v+ from the same fuse ?

  3. #3
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by robmac View Post
    1) Disconnect the alternator light at the alternator and check if the problem goes away.

    2) Disconnect the ECU feed to the tacho and see if the problem goes away.

    After isolating what is causing the issue you can start investigating why.

    I would start with item 2 fault finding.

    Are the tacho and alternator supplied 12v+ from the same fuse ?
    Thanks for the prompt reply rob.

    As I said, i'm an electrical idiot so please excuse me for not understanding first up what you are talking about.

    Re #1.
    My alt has a clump of heavy gauge wires on a threaded post and a small gauge wire on a spade terminal.
    Is the thin wire with spade terminal the alt light wire??

    Jo

  4. #4
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by jo proffi View Post
    Thanks for the prompt reply rob.

    As I said, i'm an electrical idiot so please excuse me for not understanding first up what you are talking about.

    Re #1.
    My alt has a clump of heavy gauge wires on a threaded post and a small gauge wire on a spade terminal.
    Is the thin wire with spade terminal the alt light wire??

    Jo
    The big connection on the alternator is the battery +ve terminal and where the charging current to the battery is sourced. The reason for the "clump" of other is connection is because it's a convenient place to get power for other stuff.

    The small connection, thin wire, is the alternator light terminal. The light is normally just a lamp with the other side connected to ign switched 12v+.

    The alternator "grounds" the terminal when it is not charging and hence the lamp lights up. When the alternator is charging the terminal goes to 12v+, same as the other side of lamp and because there is no relative voltage across the lamp it goes out.

  5. #5
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by jo proffi View Post
    Re #1.
    My alt has a clump of heavy gauge wires on a threaded post and a small gauge wire on a spade terminal.
    Is the thin wire with spade terminal the alt light wire??

    Jo
    I just unplugged that spade terminal wire whilst motor was running...nothing changed.
    Restarted motor...alt light glowed then went off as per usual.
    When the (correct) alt light lead is removed, should the alt light glow???

    jo

  6. #6
    1000+ Posts robmac's Avatar
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    The lamp should not light at all with the lamp wire disconnected.

    I assume it's an internal regulator in the alternator? If it's got an external regulator then it's different.

  7. #7
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by robmac View Post
    The alternator "grounds" the terminal when it is not charging and hence the lamp lights up. When the alternator is charging the terminal goes to 12v+, same as the other side of lamp and because there is no relative voltage across the lamp it goes out.
    Geez, I strugle to make mental pictures of even the most basic of electrical circuits.

    If the the alt light lead is not plugged into the alt, and the alt in not grounding the light should I see no glow at the alt light or is there another earth somewhere???(should i say...Should there NOT be another earth somewhere???)

    Jo

  8. #8
    1000+ Posts robmac's Avatar
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    See the pdf....
    Attached Files Attached Files

  9. #9
    1000+ Posts jo proffi's Avatar
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    This thread conversation has the most screwed up timing ...I need to make mental pictures and type faster.

    So the light wire when disconnected should just be a floating dead lead.
    It probably is not based on what I'm seeing at the globe, so I'll hunt around with my meter and see if i cant find where it is earthing out.
    I have my suspicions what is causing this now.


    Again, thanks for the help Rob, your pointers are invaluable.
    Earlier today imagining what was the problem was like imagining the universe before the big bang.
    Just a total vacuum of thought.


    Jo

  10. #10
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by robmac View Post
    See the pdf....

    I was thinking..OH NO, not another bloody circuit diagram for me to look at and go dizzy following little dissapearing and converging parallel lines... but that picture is clear as glass and I fully understand with a firm mental picture the circuit now.


    I'm fairly certain I've screwed up the integration of the new ecu into the fuego loom.
    Thats easy peasy to unwrap and fix , there are just 3 wires, an earth, a switched + and a tacho wire.

    I'll check and/or redo these connections and report back.

    Cheers, Jo.

  11. #11
    1000+ Posts robmac's Avatar
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    Jo,

    There may also be "tacho" output programing in the ECU software.

    It will be either "switch low" (ground) or "switch hi" (+12v)

    If there is an option, try the opposite to what you currently have programmed.

    cheers

    Rob

  12. #12
    1000+ Posts The Gonz's Avatar
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    Nice to see good progress, guys. You won't believe the technical work I get into as the Coalition's Chief of Electronic Countermeasures Operations. I'm now redesigning EOD robots (but that's not necessarily something every HQ Chief would get into - I like nerding up!). Misplaced 12V feeds and earths are like looking nostalgically at working on my Kingswood, kinda reminds me of indicators losing their earth connections and causing brake lights to flash

  13. #13
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by The Gonz View Post
    Nice to see good progress, guys. You won't believe the technical work I get into as the Coalition's Chief of Electronic Countermeasures Operations. I'm now redesigning EOD robots (but that's not necessarily something every HQ Chief would get into - I like nerding up!). Misplaced 12V feeds and earths are like looking nostalgically at working on my Kingswood, kinda reminds me of indicators losing their earth connections and causing brake lights to flash
    Wow...


    Jo

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