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Thread: Alternator wiring - lift-pump and ground

  1. #1
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    Alternator wiring - lift-pump and ground

    I had to take the alternator off to get my timing gear cover off. In the process it seems I pulled off a wire and I can not figure out where it went. The wire seems to be the ground for the lift pump since the other lift pump wire splices into the ignition circuit. The other lift pump wire is just got some bare semi-corroded copper strands sticking out. I don't see any crimp connectors missing a wire anywhere near.

    My guess is that it went to either the block, or the ground terminal on the alternator. I cut it back to clean wire and put a crimp loop on and put it on the alternator's ground terminal. What struck me as funny there was that there were NO other wires connected to that ground except for one short one that goes into the regulator (I am guessing) on the back of the alternator.

    Should there be a wire on the alternator to the block (or other solid ground)? The only other path would be from the alternator case to the block via the bracket(s) which are either painted or greasy or rusted, so none of them seem like a decent ground.

    I am hoping to start the motor tomorrow now that its all back together, but want to make sure the alt. is grounded properly (now that the lift pump is grounded to the alternator, And I have copper fuel lines... I am not sure I want my fuel tank and lines the only ground path. doesn't seem right).

    Thanks for advice in advance,

  2. #2
    Principal Partner Kenneth K's Avatar
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    Here's what the back of my alternator looked like before I removed it for the alternator bracket upgrade. Nothing, other than the regulator, was (or is now) connected to the ground post on the alternator.

    Click image for larger version. 

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    Most of my grounds were haphazardly bolted to whatever was convenient--3 to the studs on the exhaust manifold, another 3 to an exhaust flange stud.

    Click image for larger version. 

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    I think this was common practice, and it leads a lot of us to installing ground bus bars on the engine stringer.

    As to, "Should there be a wire on the alternator to the block (or other solid ground)? The only other path would be from the alternator case to the block via the bracket(s) which are either painted or greasy or rusted, so none of them seem like a decent ground." I don't think that's necessary:

    Click image for larger version. 

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    I don't think it matters much what you ground the fuel pump to, as long as it is something with a good electrical connection to the block. My choice would probably be not to ground it to the alternator ground post. What exactly is going on inside that regulator is still a bit of PFM to me, so I'd rather have my ground going directly to the block or to a ground bus bar.
    Last edited by Kenneth K; 05-19-2019 at 12:18 AM.
    Ken
    '85 E32-3 "Mariah" #641
    Universal M-25

    "Saltwater is the cure; sweat, tears, or the sea......"

  3. #3
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    Thanks,

    I ended up wire brushing the alternator bracket and the alternator where they meet. Nice shiny aluminum. Then grounded the lift pump to the manifold where there was a broken crimped wire (but the broke wire was another color, not the lift pump ground.. who knows where it went before I broke it?)

    When time permits I'll add a ground bus bar I already bought, wired to the same engine mount the battery ground goes to.

    The happy ending to this is that the engine fired right up and I ran for almost an hour on the hard and it's never run so well.

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