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Eratic Voltmeter Indications

Does anyone know why I might be getting a +/- 2 volt indication when I step on the brake pedal or turn on the turn signals? Other than those times, I am indicating about 12-13 volts. The alternator light is on very faintly at night with the headlights on (just barely noticeable). Could I have a loose wire or a ground somewhere? Any thoughts?

HUTCHWE
Old 01-07-2000, 09:48 AM
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Either the alternator is going down for the count or there is a bad ground some place....

Take the car to a place that has free alternator testing...but some of them do that all the time...

[This message has been edited by mikez (edited 01-07-2000).]
Old 01-07-2000, 10:05 AM
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I've JUST had my alternator rebuilt, new voltage regulator and battery and see the EXACT same behaviour. Thus I know that my charging system is in top stock shape.

Still at night I see a two volt drop when applying the brakes. Hell I see a two volt drop from headlights, one volt for blinkers and one half volt drop for heat blower. All that's additive as well! I remember someone on this list stating last sumer that the volt meter wasn't wired in the best circuit and lead to bad readings. IMO this would not effect a volt meter, but would effect an ammeter.

Anyway with it all rebuilt I've decided that this is the way the car acts and I'm gonna live with it. The charging system does work, so who knows?

Later
Ian
Old 01-07-2000, 10:15 AM
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The feed for the voltmeter comes from the positive line to the stop light switch. What your seeing is probably the difference in voltage due to the resistance of the wire when ever a load is applied (remember Ohm's law). Brian is right on as mine did the same.
Old 01-07-2000, 11:00 AM
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Well my alternator in my 914 is a stock 911 unit that came with the 3.0. It drops a very tiny bit at idle and when starting, when all the lights are on as well as the stereo.

It is a higher output unit than the four cylinder ones....BUT, I have my voltmeter wired direct to the battery...it never goes below 12 volts. It is not the best thing to do 'cause you run the risk of draining the battery unless it is driven every day.

If in the garage for more than three days, hooked to the trickle charger, at the airport, the negative post is disconnected...so you might get a better read on the meter if hooked directly...
Old 01-07-2000, 12:37 PM
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Hmm.. i've got a new VR and a alternator (6 months?) and i get a reading of 14v while driving on my autometer gauge. 13.5+/- with headlights, 13 with foglights, 12v with the fan for the oil cooler on, and pulsates between 11 and 12v when my stereo is draining 900W out of the system.. (need a cap)..
my light doesn't come on until i drop below 12.5..

Jeff
Old 01-07-2000, 02:09 PM
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So Jeff, with a 900 Watt stereo in your 914, you don't even need the engine to propell it right? You could probably just leave the key out, locking the steering wheel, and use the balance control on your stereo to steer right and left. ;^)
Old 01-08-2000, 12:41 PM
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Yes, it really is where the meter is in the circuit. When there's any dirt or corrosion or burning of any of the contacts in the circuit, the voltage starts dropping when there is a load on the circuit. Since the voltage comes directly from the ignition switch, on the same terminal that feeds the brake lights, the headlights, etc., almost all stock 914 voltmeters show this behavior. If you want a *real* reading on the health of the charging system, either do as Mike Z. did and wire directly to the battery, or dig out an external voltmeter and measure directly across the battery terminals.

--DD
Old 01-08-2000, 05:26 PM
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