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Grounds wiring: 90-93 NA 1.6 ground junctions JC-02 JC-03

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  • Grounds wiring: 90-93 NA 1.6 ground junctions JC-02 JC-03

    Hoping somebody has some familiarity with these. On my Miata there was a jumper wire installed between these two where they ground at the head (OE I think it's on intake manifold on bracket?). The jumper did not look factory in my case- it was crammed inside the harness cover and taped up. In the interest of noise reduction I removed it to separate the power and sensor grounds. OE, JC-02 is the ground junction for the sensors, and JC-03 is for power, BUT for some reason they're connected. In the shop manual diagram below, the highlighted area shows this connection. What I'd like to know is IF that connection is the one I remove (are they jumped at the engine/intake manifold) or does this happen somewhere else? thanks!

    | 90 Miata | Turbocharged Stock Mazda FE-dohc 2.0L engine swap | 302whp 281ftlbs |

  • #2
    I'm trying to remember, but I recall there are some grounds spliced/jumped together on the pigtail that goes to the ECU. I found them when I unwrapped that portion trying to chase electrical issues, which kind of surprised me a bit. I have a the old front harness from my car in a box out on the garage.

    I combined the ground point for those in the engine bay by using the same bolt. I ran a new ground strap from there to the body as well. There is a corresponding strap I also installed similarly on the drivers side.

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    • #3
      Thanks, that helps- I'll look at the harness at the ECU, following the ground leads out from the connector. The condenser at the ignitor is also connected to JC-02 at the igniter - which is also noise suppression. The noise I have is at high rpm/load - which is why I suspect this connection with the coil.
      | 90 Miata | Turbocharged Stock Mazda FE-dohc 2.0L engine swap | 302whp 281ftlbs |

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      • #4
        I made big, meaty common grounds from battery cable, then later from flat, braided SS that attach to the motor and body. I'v been running that since I started dabbling in stand alone ECUs many years ago. It helps with the noise you're describing and all the nagging grounding issues these cars develop over time.

        if there's a section of harness you cant get at or don't want to unwrap, let me know. I can try to photograph it from my spare.
        Last edited by kung fu jesus; 04-25-2017, 11:46 AM.

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