348 "Electrical wonderment" question on Oil Pressure gauge | FerrariChat

348 "Electrical wonderment" question on Oil Pressure gauge

Discussion in 'Technical Q&A' started by NC348, Dec 15, 2003.

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  1. NC348

    NC348 Karting

    Feb 18, 2003
    Houston, TX
    Full Name:
    James I. Movich
    OK, this one is in the "too hard" box. i need some help.

    when i turn on my headlights, my oil pressure drops?!?!?!?!?

    Normally runs @ just over 70, ....... turn on the lights, and it drops to ~50 or so. anyone have ANY idea where to start with this?
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    (If you mean the RPM of the engine doesn't change enough to cause the drop then) One thing that can contribute to this effect is a poor ground from the gauge to the chassis if that gauge's ground connection is also used for its internal lamp ground -- i.e., when you turn on the headlamps, which puts +12V on the gauge lamps, the whole "ground" network of the gauge (or instrument cluster) can be "pulled up" a bit (to like +0.3V) relative to the true chassis (0V) ground. Usually it's a "half-a-needle-width" type change so can be ignored, but your reported change seems more significant.

    I don't know the specific wiring architecture of your 348, but usually the connection from the chassis ground to the instrument cluster ground is a tenuous maze of bolted/flaky connections (that often have too much paint IMO). Is it only the OP gauge that changes its reading? If it's got an independent ground network connection it might be worth checking (although the first thing to do is measure the voltage at the battery terminals, engine running, with headlights on and off just to make sure it doesn't change too much -- i.e., the alternator system is quasi-healthy)...
  3. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    Full Name:
    Malcolm W
    Does this only happen when you turn on the headlights, or are there other electrical components that have the same effect ie :(wipers, indicators etc.)

    The problem will more than likely be a poor ground connection, try looking around the relay / fuse board area, I recall that there is a "common" grounding point there.

    If the problem becomes more in depth and you need wiring diagrams I will post them for you.

  4. ricrain

    ricrain Karting

    Nov 1, 2003
    Dallas Area
    Full Name:
    Maybe the headlights burn oil for light, like in the old mining days. My 20+ PSI?? hehe

    Check grounding on the gauge. It's not likely to be grounding at the sender, but it would be easy to test. You're best bet is to run an alternate ground from a known good ground source to the points in question.
  5. Spasso

    Spasso F1 World Champ

    Feb 16, 2003
    Land of Slugs & Moss
    Full Name:
    Han Solo
    According to the old Fchat archives the oil burning headlights were used on GT4's destined for the middle east. ;-)

  6. NC348

    NC348 Karting

    Feb 18, 2003
    Houston, TX
    Full Name:
    James I. Movich
    i must say.... i did not think about the lights burning oil, increasing the consumption rate, and thereby lowering the pressure by an equivilant amount.....Shame on me! ( i will try the high beams next, and see what happens).

    So far, the only time i have noticed it is the lights. thanks all for the grounding tips, i'll start there......

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