Quote:
Originally Posted by greg_gorrell
Okay here's something interesting I just figured out. When testing the positive wire going into the alternator from the starter, with the neg. probe on the battery post I get nothing. When I disconnect the negative post from the battery and check the same wire with the neg. probe on the battery itself I get ~13 volts. I then hooked the battery back up, one probe on various parts of the engine, pos probe on battery and im getting around 13 volts again. It seems there is something with my negative battery cable that has something to do with it. I dont understand why it will make a full circuit on the battery itself, but when the batter is hooked up and i check on the post, theres nothing. I have nothing shorting out and the battery doesnt drain unless the car is on. What am I missing here?
I took a pic of the wiring diagram and will post in a few minutes when I find the cord.
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whoah whoah whoah, ok, there's something very important you have to know about measuring voltage.
*When there is a break in the circuit (ie ground removed), you will always find voltage across that break!*
When you take the ground off, and put one lead on that neg post, you're measuring across the break, thus system voltage. If you were to put your voltmeter leads on the negative cable and one on the negative post, you will read system voltage.
That's very important to know. So is this:
The voltmeter measures drops in voltage.. or difference. When a circuit is closed and working properly, loads (resistance) with current through them "use" voltage so to speak. If you have two identical light bulbs in series, one will "use" 6V, and the other will "use" the other 6, leaving almost nothing at ground (it'll be a very minute reading, in reality). Measure across one bulb and you'll see 6 volts, because the 2 voltages will be 12 on one side, 6 on the other. Hope that makes sense.
NOW, remove ground after the 2nd bulb. No more current can flow, THUS, there's no voltage drop across the bulbs. If you measure across the break in ground you will still see 12V, because the voltage "pressure" is still there, and no current = no voltage drop across loads.
Ok i'm gonna double post here.. stay tuned.