Does the volt meter in the car register voltage from the battery or directly from the alternator. Using a voltmeter I just go black to ground and red to the positive terminal on the alternator that leads to battery, and I think this should give me my charging current, is that correct. Then I would do the same but at the battery positive terminal. What about the old test of pulling a battery cable to see if the car continues to run and if not its the alternator?

The volt meter tells you what the alt is charging and most likely
if the battery is been discharged an you just put a charger an it just to get it started the alternater will charge more then normal or if your using alot of juice like radio with amp and subs with other goodies

Yeah thanks I just revamped my whole system battery alternator, wires to the gauge. The wire that leads off the alternator that controls the internal regulator fried and it was giving bad signals and the alternator was cooking everything. All clean and new now.

You really dont want to do the old pull the battery cable trick on a cpu controlled car. The battery is a shock absorber for all the voltage spikes that occur. Doing that can fry an ecm.

checkign voltage at battery with car on, should read above 12.5 if charging. mine is like 14.2.

I thought it was suppose to be just above 13.something. Okay, here's another stupid question - voltmeter vs. ampmeter. Isn't the ampmeter the one where it sits in the middle, CHARGING is on the rigt and DISCHARGE is on the left of the middle?

Your battery should read about 12V when the engine is off and just over 13 when it's running.

M@

Yeah it interesting some of the basics you learn when tampering with stuff. Basically I couldn't figure out what was going on because my readings seemed OK even though my alt & battery were being fried. Biggest problem the average Joe will have trying to test this stuff is I couldn't get a good reading under load and thats when things were going haywire. I was getting a solid 11.8 reading from the battery when it was disconnected seemed like that should have been fine. The Alternator was also reading right around 12 with the car at idle. Thats where I was getting confused not knowing when the car is running and I am taking the reading from the + at the alternator what was I actually checking and it could be your alt or battery depending on if the Alt was fried you would get a straight voltage reading that the battery was giving because its connected into the circuit. Only under load could I have seen if there was a flucuation with the voltage. Anyways as mentioned before the real culprit turned out to be one of the other wires (I think the brown one) that runs off the alternator and regulates the voltage the alternator puts out.

The voltmeter on 88 Iroc was acting real weird so I bought one of those voltmeters that plug into the cigarette lighter. Now I can monitor the voltage with confidence instead of watch the dash gauge jump all over the place.

Well if your voltage is actually good but the meter is all over its propbably a short or bad connnection with one of the three wires that run off the back of the alternator. I forget which one and don't have my book but one of those runs into dash gauge. There is a test you can do with a voltmeter to see if the lines good. The three wire plug at the back of your alt. can be unplugged then you test the line, it should read like .5V I can't remember exactly if you really want to know I will check the book for the exact reading and get back to you. Let me know.

MANY things can cause the dash Volts gage to act weird. Here are a few:

Dirty fuse connection.
Dirty ground connection.
Bad conection between the gage and the dash circut board.
Dirty ignition switch contact.

You should always read the same voltage at the batery as at the alt output, they are tied directly together by a wire.

NORMAL voltage with car ON= 13.5-14.5 volts
OFF=12.5 volts.

I am not real concerned about fixing the dash gauge now that I got that cheapy cig lighter voltmeter. It matches the gas gauge, which tends to jump around. Of the possible causes, I would say Bad conection between the gage and the dash circut board or a bad connection at the alternator. I did change the headlight switch last summer. That was a real PIA to do. Other then the gas gauge, there is nothing else wrong with the electrical system. Maybe if I get ambitious, I will look at it this spring.