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Thread: Oil pressure sending unit

  1. #1
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    Oil pressure sending unit

    Snow and freezing rain in Wisconsin, which is perfect weather for hanging out in the garage and getting back to my project. As I tell people that ask where I am in my roadster (complete kit) build, my response is often that life seems to get in the way. Well, I'm between other projects so I'm looking forward to some quality time on my car. I'm hoping to have it in go-cart stage and take a few laps around my neighborhood by early spring. Maybe even sooner.

    Starting out the morning with a simple question. Do I need to ground the oil pressure sending unit supplied with the speed hut gauges or, is it grounded thru the threads? The oil pressure gauge comes with wire that plugs to the back of the gauge with white and black wires to be secured to the sending unit at the two sending unit terminals marked "S" and "G". But, I chose to use the single gray wire within the Ron Francis wire harness labeled "oil pressure". So...do I need to ground the "G" terminal to the block? If yes, any thoughts as to where?

  2. #2
    Senior Member edwardb's Avatar
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    The Speedhut 2-wire oil pressure sending unit needs signal and ground at the terminals. Unlike some other sensors, it's not grounded through the threads. Other Speedhut gauges are also 2-wire, and you're right, the RF harness only has the single signal wires for the gauges. I add ground wires to the sending unit harness and connect them to chassis ground behind the dash. You could connect something closer, e.g. nearer the sending unit(s) if that's your preference.
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    Quote Originally Posted by edwardb View Post
    The Speedhut 2-wire oil pressure sending unit needs signal and ground at the terminals. Unlike some other sensors, it's not grounded through the threads. Other Speedhut gauges are also 2-wire, and you're right, the RF harness only has the single signal wires for the gauges. I add ground wires to the sending unit harness and connect them to chassis ground behind the dash. You could connect something closer, e.g. nearer the sending unit(s) if that's your preference.
    Excellent solution. I can always count on you to come thru. Now, back to the car, with one eye watching your paint progress.

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    Well Used Member boat737's Avatar
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    I had a boss on the intake manifold, that I used for two purposes. I installed a stud into it, then used that for my throttle return spring mount, and also a grounding stud. I have grounds from the water temp, oil press, distributor, choke, and a 10 ga. wire running from it to the block grounding stud that connects to the battery and chassis. The intake manifold seemed to be well grounded and have good continuity to the block and chassis, but I wanted to be sure, so that's why the extra 10 ga. wire from the grounding stud to the block grounding point. That grounding stud is a very good place for all my grounds on the engine, a nice, convenient location.
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    Last edited by boat737; 01-11-2017 at 10:17 AM.
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    Senior Member 3yearplan's Avatar
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    Can aluminum be used as a ground? Meaning the manifold, not the bolt used. I thought it had to be steel, free of paint.


    Mike
    Mark IV 7923 arrived 11-14-12
    DOHC 4.6L, Tremec 3650, 3 Link 8.8 w/3.73

  6. #6
    aluminum is fine.
    Mike

  7. #7
    Well Used Member boat737's Avatar
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    Quote Originally Posted by 3yearplan View Post
    Can aluminum be used as a ground? Meaning the manifold, not the bolt used. I thought it had to be steel, free of paint.
    Mike
    As Mike E says, it's fine. In fact, some houses (older) have aluminum wire for stuff like air conditioners. Copper is better though. And of course, bare metal, no paint.
    If Brute Force doesn't work, you're not using enough of it.
    Bought a partially completed MK4. The Basic Stuff: MK4 Complete Kit #8439. The Extra Stuff: Wilwood's, 17" Halibrands, Stainless brake and fuel lines, Breeze cooling and Battery mount.
    The Old Fart Stuff: Heater, Seat Heaters, Footbox Fresh Air, Stereo, Keyless ignition, Power Steering, Hyd Clutch.
    The Young and Dumb Stuff: 427w Dart, TKO600, 3 link Moser M9/Ford 9", 3.5:1, Eaton TruTrac Posi

  8. #8
    Senior Member karlos's Avatar
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    I believe adding a dedicated ground for the engine sensors is good advice, and I went with that approach on my build as well. I too debated whether it was best to use the RF signal wire and add a ground, or use the harness thatís supplied with the Speedhut gauges instead. I had some discussion with Kleiner on this in a previous thread and his suggestion was to use the Speedhut harness as itís a high-quality, shielded piece that makes for a clean OEM look. So thatís what I did.

    In looking at the instructions that come with the Speedhut gauges, this is what I found. Note the part in the box at the lower left. Says the sensor is grounded to the engine block through the threads.





    However, the Speedhut harness includes a ground wire that runs from the sensor to a connector on the gauge itself. A quick check with a voltmeter confirmed continuity between the sensor ground wire and the gauge common ground (black lead on the 3-wire pigtail shown in the figure). So if installed using the supplied harness, the sensor has a ground path through the gauge.

    Just for fun, I also checked to see if the sensor is in fact grounded through the block when installed as recommended using liquid sealing compound. With the Speedhut harness installed on the sensor, I checked the resistance at the end of the harness remote from the sensor. I then added a test lead from the ground terminal on the sensor directly to the negative terminal on the battery and rechecked the resistance at the remote end of the sensor harness. Got exactly the same reading. So the sensor was in fact grounded through the threads.

    All that said, I still believe a dedicated sensor ground is the right way to go. Just wanted to point out that the Speedhut harness provides that functionality without having to modify anything. And that you likely have a redundant ground path through the sensor threads as well (if installed using liquid rather than tape).

  9. #9
    Senior Member 3yearplan's Avatar
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    aluminum is fine.
    Mike

    As Mike E says, it's fine. In fact, some houses (older) have aluminum wire for stuff like air conditioners. Copper is better though. And of course, bare metal, no paint.


    Well, now I know. Thanks gents.
    Mike
    Mark IV 7923 arrived 11-14-12
    DOHC 4.6L, Tremec 3650, 3 Link 8.8 w/3.73

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