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Mysterious Grey Wire (Fuel Pump)

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  • Mysterious Grey Wire (Fuel Pump)

    A few weeks ago I made a modification mentioned here regarding the power control to the fuel pump, that is to rewire the ground wire from the pump directly to chassis ground instead of having it be controlled by the ECU. A blue Nissan relay (new) was installed where the coil was inserted in the circuit where the pump would be and a wire (30 amp fused) from the battery now was the source of a steady +12V. But my question is, does anyone know what a third grey wire in the harness is used for? It goes along with the 2 main power wires to and from the OEM connector to the pump under the rear carpeting. And here's the strange part ... it's thin coax. The center conductor is way too thin to carry pump current ... I'd guess around 24 - 28 AWG. And it shows continuity to chassis ground. The shielding connects to nothing, no continuity at all with anything --- just shielding. And it isn't in any of the manuals, Haynes or the FSM. Does anyone know of this wire? ... or has come across it?

  • #2
    I thought all the shields went direct to ground. Run a continuity check on it to verify.
    71 240z

    80 280zx 10th Anniversary

    88 300zx Turbo, 89 300zx Turbo

    Datsun Jeff


    • #3
      I did, and it was essentially open. Meaning it was there around the dielectric surrounding the thin center wire, but not connected to anything, such as ground. It was the center wire that showed continuity to ground. And this grey wire overall was thin, like 14 or 16 AWG thin. Yet it clearly was coax (when cut and opened). And it went into the fuel pump connector along with the other two power lines, and out towards the pump. That connector also has three (3) pins, although all the manuals only show it as having 2: the ground (black) and +12V (striped). I'm stumped. And so was my friend (who's an EE) that helped me do the mod.

      In the end we decided to merely terminate it, tape it up and ignore it. No one ever mentioned it being there and it wasn't in the manuals, so we assumed for our purposes it to be non-essential. So far that seems to be the case, as all is working as it should.


      • #4
        My car had the same and I too terminated it when I installed my Walbro years ago. It had no effect on the pumps operation while i used it.
        Originally posted by Andrew84zx
        tell her your car is so fast it will make her panties fly off
        545 RWHP & 540 RWTQ Member


        • #5
          Ignore it and wire it logically.
          Straya, +61