Gauges climb slightly when headlights are on 308? | FerrariChat

Gauges climb slightly when headlights are on 308?

Discussion in 'Technical Q&A' started by 308GTS, Feb 18, 2004.

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  1. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    On my 308 QV when I turn my headlights on the gauges all increase slightly. (approx. 1/2 the distance between the marks on each gauge) I went through my fuse blocks and none were hot and they are fairly new so I am thinking this isn't the culprit in this case. I know others have had this problem but was it anything else besides the fuse block? Any other items to check? Thanks.
  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
    Check the grounding of the instrument cluster -- if the ground plane of the instrument cluster floats up relative to a good battery/chassis ground with the headlights on you've got a poor ground connection (and it's a flaky design to start with ;)).

    Alternatively, you could try adding another known good electrical connection between the instrument cluster ground and the chassis ground to see if it improves things.

    I wouldn't worry about a "needle width" change, but your description seems it's more than that.
  3. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    Yes it is a little larger than a needle width but not by much. Thanks for the info.
  4. thecarreaper

    thecarreaper F1 World Champ
    Silver Subscribed

    Sep 30, 2003
    i had a bad amp gauge once that was coupled with a ground problem in the steering column. i found the steering column problem as the wiring caught on fire!!!!! for goodness sake check your wiring with a meter! dont let another fcar turn in to a candle. perhaps you can take voltage and resistance readings as you remove fuses and disable circuits until you identify which SYSTEM the problem may be in ( ie gauge circuit).
    i also fixed a identical situation in a car that had a bad / shorted dome light circuit. one of the many little interior lights was shorted TO POWER not to ground. the bulb was burned up and the socket melted, and it had a " parasitic draw" ie it ran down the battery. wiring is so much fun!!!
  5. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    Great point. I was all over my car with a Multi-Meter today. I didn't find anything unusual so far. I checked my gauges again and it is about a needle width so maybe it is normal but I am going to clean and check my grounds. I will recheck the fuseblock tomorrow. I will also check my gauges/connections. Thanks Again.
  6. Zanny1

    Zanny1 Formula Junior
    Silver Subscribed

    Dec 19, 2003
    Full Name:
    Had the same problem on my '84 308 QV. Did everything described in replies with no luck in fixing the problem. One thing I noted was that the needles would not move up on the guages (all of the small guages in the central insrument cluster) when the ignition was turned off. Also, the two small guages in the console never seemed to have the problem.

    Good luck.
  7. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    Irvine CA
    Full Name:
    To rule out a problem with the alternator, turn the lights on and off while the car is not running.

    I had electrical problems in my '76 308 for years - lights would dim unexpectedly then go very bright. Had the alternator rebuilt and the problem went away.

    Also found wrong bulbs in the side lights which affected the electrical system.

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