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What causes the needle on the voltage gauge to move down and back up when I use the blinkers or anything electrical such as the blower fan,headlights etc. Battery is new alternator is 2 yrs old PROSTA

Wondering if the reulator has went bad in the 2 yr old alternator? Its a brand called Prostart

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Go to autozone,they will test both for free.

Posted on Nov 12, 2014


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How does the gas gauge work on a 1985 Cadillac el dorado

On them older cars (and maybe still to some extent) they had a tiny voltage regulator on the instrument cluster board, just before the gas gauge and the temperature gauge. It cut the voltage going through those two gauges to about 5-7volts, before sending the signal out to the sending units.
For the in-tank sending unit, it had about 5 volts current running from the dash to the sending unit. The float on the sending unit attaches to a "variable resistor", and then goes to ground. What the dash gauge measures is the "resistance to ground", and is thus translated to the needle on the gauge showing anywhere from empty to full. Pretty neat, huh?
So if you are working on the gas gauge, you would check for that small voltage at the fuel tank electrical connector. Folks used to test whether the gauge or the sending unit was the problem by taking the wire at the tank and just temporarily grounding the wire to a ground, a clean metal piece of the frame down there. If it caused the needle to move AT ALL, then you would know that the problem is not the dash gauge, but the sending unit in the tank. Get a helper to watch the needle while you ground it. Careful not to let it ground too long-you can damage the gauge or voltage regulator. You just want to touch it to a clean piece of the frame while someone watches for needle movement-even just a little movement. Often this test would cause the needle to jump to full, or maybe just halfway, but any movement of the gauge needle means the gauge is okay. For this test, the ignition key must be on (not start, not engine running, just key in on).
The variable resistor on the sending unit is a little flimsy, and easily disrupted-that is why so many failed. A new one should not be very expensive-it is all one piece. You don't buy a separate resistor, you just buy the whole apparatus with the float and arm attached.
Probably 80-90% of the time, when the gas gauge stopped working, it was the sending unit, not the gauge itself.

May 24, 2017 | Cadillac Cars & Trucks

3 Answers

Heat gauge needle pointed the wrong way. Catches on fuel gauge needle

I have fixed speedometer and RPM gauges before. Never had the temp gauge do this. You have to remove the instrument panel and rotate it clock wise. Watch the needle and see if it moves. If it does, take it back to the original position. I check them with a scanner. But they seem to work right. The just have glitches sometimes that drives the needle to the other side.

May 16, 2016 | Cars & Trucks

1 Answer

Hi ihave a 89 toyota surf v6 conversion can enyone tell me why when i turn on thefan and the heater gauge moves/the a/c button also moves the gauge on dash,are they a separate problem or could it be s

oh what and old car, (my fav)
this is now a custom car, that makes all factory books useless.
so find a shop that will touch it, good luck finding that , many will not. (risk big time)

i can tell you the wiring to the dash cluster is bad.
the converter was hack job. he overloaded the circuits.
if you learn electrics, youd, have checked the voltage a the cluster
power pin, then with fan on, see it do like a rock.
2 causes, bad wiring (small) or blower motor overload (wrong blower or partially shorted inside)
or corroded power feeds, and any place forward
a pro electric shop can find the voltage drop and cause.
i could in 5min flat.

Jan 14, 2015 | Toyota Cars & Trucks

1 Answer

1993 Dodge Spirit V6 Short?

Sounds like an alternator problem. Check belt to make sure it's tight, then have alternator tested.

Jan 06, 2010 | 1993 Dodge Spirit

2 Answers

Charging gauge bouncing back and forth starts after jump

sounds like a shorted field in the alternator

Nov 07, 2009 | 1981 Ford F 150

1 Answer

Tempeture hand on gauge rises and falls as you accelerate and slow down. Also rises and falls when you turn on the internal blower in the car. The engine does not appear to be overheating.

The problem you describe is likely being caused by the dashboard earth (ground) reference moving as the 12v power system current draw changes.

Ensure battery terminal post connections are in good order, clean and firmly connected,
Ensure the all chassis, alternator, engine and dashboard ground connections are intact and in good order.
Ensure all dashboard loom connections are properly connected,
Check alternator output voltage (battery terminal voltage) is approx 14.5 volts with engine running, while loaded with headlights or blower motor running.

If all above is ok, the dashboard internal voltage regulator supplying the instruments may be faulty (unlikely - do all other checks first).

Oct 13, 2009 | Hyundai Santa Fe Cars & Trucks

1 Answer

Electrical issues i have no lights

Sounds Like A SHORT in HeadLight Switch

Jun 02, 2009 | 1986 Jeep Cherokee

1 Answer

1992 dodge spirit turning on headlights causes horn to blow

What you describe could very well be a ground wire that is broken or corroded,check for missing or broken as well as "green" connections

Dec 13, 2008 | 1992 Dodge Spirit

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