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Old 08-19-2003, 06:54 PM   #1
Porkchop-WRX
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Default Headlights go on...oil pressure guage goes crazy

The needles just pins past 100 psi. It only happens when I turn on the headlight switch. The only thing I can think of is that I tapped the ground for the oul pressure gauge with the same ground that used to be for the light in the stock guage. This way i can contol the brightness. It works perfectly fine with the lights off. I always thought a ground is a ground no matter what but not the case here. can anyone suggest why this is happening?
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Old 08-20-2003, 01:58 AM   #2
quynce
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A ground is not always a ground, especially in a negative dimmer wire. The negative voltage varies with the dimmer. However, a chassis ground is always a chassis ground, and you can't go wrong with that.

josh
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Old 08-21-2003, 02:11 PM   #3
Porkchop-WRX
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Yeah the dimmer ground must be messing with the guage. I completly overlooked that. I always thought that the dimmer was controlled by the amount of voltage sent through the power wire. Oh well can you tell me a good spot to get a chasis grounding point somewhere near the front of the car. Maybe I can just pull it from the radio ground.???
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Old 08-21-2003, 04:37 PM   #4
satrya
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As stated, the "ground" for the stock gauge actually varies with the dimmer switch.

Quote:
Originally posted by Porkchop-WRX
..can you tell me a good spot to get a chasis grounding point somewhere near the front of the car. Maybe I can just pull it from the radio ground.
Most metal connected to the chassis gives you the true ground closest to the potential of the negative terminal of the battery. It may not be a strictly noise-free ground, but for grounding a gauge, imho, it's not that critical. Iirc, I've tried placing a multimeter's negative probe to many metal parts of the chassis with the positive probe to a constant 12V line and getting about 12V reading. You can also tap the ground line that connects to the stereo harness.
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Old 08-21-2003, 04:52 PM   #5
quynce
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I wouldn't recommend using the radio ground because you'll increase your chance of inducing noise into your system. There is plenty of metal behind the radio and under the dash.

josh
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Old 08-22-2003, 10:52 AM   #6
Porkchop-WRX
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Anyone that have a good suggestion for a chassis ground. Maybe someone else who has the center mount defi style pod can tell me where they grounded there guages.
Thanks,
Danny
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