Turn headlights on... Oil temp gauge jumps to max? | FerrariChat

Turn headlights on... Oil temp gauge jumps to max?

Discussion in 'Boxers/TR/M' started by rpissm, Aug 17, 2014.

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  1. rpissm

    rpissm Formula 3

    Aug 11, 2013
    1,620
    Salt Lake City, UT
    Full Name:
    Joe
    #1 rpissm, Aug 17, 2014
    Hey everyone,

    Here's a bit of a strange thing. Drove my TR for the first major time at night last night. I look down at my gauges and my oil temp gauge is spiked past 280. After my requisite freak-out, I remember the only other time that happened was when I was driving near my house... At dusk. So I turned off my headlights and, tada, my oil temp gauge went back to normal. Oh also, I noticed my water temp gauge had moved up as well with the lights on (from the left side of 190 to the right side of it). After turning off my headlights, it went back down to the left side of 190. Do you guys know offhand whether any circuitry is shared among those systems, or do you think something is wired wrong on those gauges?

    Thanks!
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,144
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Aug 17, 2014
    Last edited: Aug 17, 2014
    Yes, the gauges and the instruments lights share their ground connections (it's very common for the gauge needles to move a little when you turn on the parking/dash lights -- like what you describe for the water temp gauge) -- most likely, you have a bad connection somewhere in the ground network of the central tunnel (like the ground terminal connection being loose on the back of the oil temp gauge), but the fault could be internal to the oil temp gauge itself.

    Does the fuel level gauge also swing to "full" when you turn on the exterior lights and the oil temp gauge goes to max (it uses the same ground so, if it isn't misbehaving that clears all of the upstream ground connections)?

    Another easy thing to try (if the fuel gauge is misbehaving too) is just unplugging/reseating the w and b connectors on the fuse-relay panel (that's where the ground to the central tunnel comes from).
     
  3. rpissm

    rpissm Formula 3

    Aug 11, 2013
    1,620
    Salt Lake City, UT
    Full Name:
    Joe
    #3 rpissm, Aug 17, 2014
    Ah! Makes sense! Thanks for the info Steve!

    The fuel gauge stays put. I also noticed that the light behind the Oil temp gauge is burned out. Something suspicious?
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,144
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #4 Steve Magnusson, Aug 17, 2014
    Last edited: Aug 17, 2014
    Yes -- indicates that the ground connection to the gauge/light is broken/loose (typically, these instrument bulbs are way over-designed so that they don't burn out -- even over the whole typical lifetime of a car).
     
  5. rpissm

    rpissm Formula 3

    Aug 11, 2013
    1,620
    Salt Lake City, UT
    Full Name:
    Joe
    #5 rpissm, Aug 28, 2014
    Hey everyone, just thought I'd let you know that I fixed the problem! I took the oil temp (and fuel) gauges out and discovered that there was a missing ground wire from the yellow lamp lead (wire colored black was missing). I hooked up another wire from that ground terminal to the ground on the fuel gauge and tada! The gauge stays put AND now the gauge light works!
     

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