I have a problem, but I am not sure if it is with the alternator or the battery or some other electrical problem. When I am driving my voltage guage shows anywhere from 10 at the lowest to 14 at the highest. It drops down about 3 volts when I turn the heat/vent fan on. If I put the car in gear and sit there it hovers around 12V. I can rev the engine and it will jump up to 14V, which is where I recall it always was. If i put it in park it goes back up to 14V. While I am driving it will sit around 12V but sometimes jumps very quickly to 14 and then back down. I have no idea what is wrong with it.

 

A 3 volt reading suggests possibly the instrument panel has a bad copper strip somewhere. The instruments. lights etc, pierce the plastic cover of the copper, and then contact the copper. Sometimes the copper breaks, or the contact goes bad.

What can happen, is the power finds another route to where it is supposed to go, and that can be through a light bulb, another instrument or a switch somewhere. That can give weird readings on all the guages.

Before you rip out the panel though, just put a voltmeter on the battery and see what it reads.

 

It doesn't drop to 3 volts, it drops 3 volts. So down to around 10 or 11. I was driving more today in the city and it stayed around 12 or so while i was driving, still dipped and peaked at stoplights though...

 

Opps I see what you mean, I read it went down to 3. Did it always do this, or did it just start. Do the headlights dim at night when the guage shows lower voltage?

 

I don't notice the lights dimming at all, I just noticed it recently. AS far as I remember it was always rock solid @ 14V and never varried.

 

It sounds like you could maybe check the voltage with a voltmeter. Check at the battery and at the aternator, with the engine at different speeds. Then if that is steady you need to test at the fuses which supplies the instrument guages.

If teh battery and generator are OK, but the voltage at the fuse changes there may be a resistance in the line somewhere.

 

I tested the battery, it is 12V with the car off. 14.4V with the car running in idle and 13.98V steady with the car in gear and the heater and fan on high(and a amp with subs on too). The gauge was showing 10V or so, moving up and down a little at the time. What wires/pins do i need to check at the alternator, and what fuse is the Instrument pannel fuse? My fusebox pannel with the chart is long gone.

Thanks.
CHris

 

There doesn't seem to be anything wrong with the alternator or the battery, and so long as you don't notice the dash panel lights dimming at night, is doesn't sound as if there is anything wrong with the supply to the instrument panel either. It sounds mostly like guage is on its way out and over responding to a slight change in the voltage.

You say it would suddenly jump, so it could just need it's terminals cleaning, they are just clips that slide over rods. or it could need replacing.

If you can get upside down, looking up at teh fuse box, it should have the fuse names on it.

The guages fuse is 10 amp. go to the row on the opposite side to the circuit breakers. go to the middle of the row and it is there.