Should my volt meter read 0 when key is off?

['70_402]

hey all, long time no post for me. i'm back with a ? i installed a painless wiring harness about 2 years ago and have had no wiring troubles untill now... when i turn my key off should my volt meter go to 0? i think it should, but i have disconnected everything i own on that truck and nothing gets it to 0 other than disconnecting the negitive battery cable..... what gives.... i looked at all my wires and don't have a cut or a bare spot on any of them.... i replaced my voltage regulator and even unhooked the pigtail to the back of the key switch.... any ideas.....

thanks

rick

[eedgell]

Your saying that it used to go to "0"? With key off?

['70_402]

Originally Posted by eedgell

Your saying that it used to go to "0"? With key off?

thats the thing..... i can't remember.... i might just be freakin myself out.... but my thinking is if i have nothing else on.... why would it be reading 12 or 8 volts.

[Longhorn Man]

if you have a voltmeter, then it is aftermarket, and it needs to get plugged into an acc position in the fuse box.

[GREASEMONKEY72]

Originally Posted by Longhorn Man

if you have a voltmeter, then it is aftermarket, and it needs to get plugged into an acc position in the fuse box.

[Rupdog]

also make sure the door is closed, or the dome light will show current draw. i know it's obvious, but it's also worth mentioning...

[eedgell]

My after market tach does the same thing in reverse. Stays at 800 rpm untill I turn the key on, then it returns to "0".

['70_402]

Originally Posted by eedgell

Your saying that it used to go to "0"? With key off?

Originally Posted by eedgell

My after market tach does the same thing in reverse. Stays at 800 rpm untill I turn the key on, then it returns to "0".

that is understandable.... tachs work that way.... i have all autometer guages and my tach does that, that is not my problem.... i am trying to trace down a wiring gremlin... and i need to know if my theory is correct about the volt meter..... i have it hooked up in the correct spot, in the painless wiring harness there is a wire for the volt meter.

[eedgell]

You still never answerd if it used to read "0" before your trouble. Having said that, the meter cant read unless the power is running through it. So with every thing off, power must still be going through the gauge to ground, or flowing. It only reads what "flows" through it. Does your battery go dead? If not it might be a bad gauge.

[Rupdog]

off the top of my head, these things draw current when the key is "off"...

1 - aftermarket stereo (memory settings and clock draw current)

2 - dash clock, if installed.

3 - car alarm?


disconnect the negative cable, and put your ohm meter in series between the neg cable and the neg post. if you see current flow, either neg or pos, then pull one fuse at a time out of the fuse box until you see zero battery drain. once you've found the faulty circuit, you can narrow down your search.

someone chime in if i'm soundin' crazy here.

[GREASEMONKEY72]

kinda sounds fine to me as in when the key is off theres no voltage going through it hence it reading zero and when you turn the key on its got voltage again and reads 12 volts, atlest thats my guess, the gauge in my truck stays in the middle on or off but IIFR the stock gauge is a ammeter and not volt

[Longhorn Man]

he verified it's an aftermarket volt guage... so all this current talk is moot.
Turn off the ignition, verify your guage says 12 volts or so. Then, disconnect the battery. If it still stays on 12, then the guage is made to do this, like some (not all) tachs as mentioned before.
If it drops, then you'll need to find a switched source to feed the guage.

[eedgell]

Sounds right to me Longhorn Man!!!!!

[72lb4x4]

Whether or not other things are turned on, such as lights makes no difference to a voltmeter. With 0 volts applied to the meter, it should read 0 volts.

Voltage is applied to a load.
There is no such thing as "voltage going through" a load.
Current flows through a load.
A load draws current based on the resistance of the load.

Think of Electromotive Force, measured in Volts, as water pressure,
current (intensity), measured in Amperes (Amps), as water flowing,
and resistance, measured in Ohms, as restrictions to the flow of water.

E=IR or V=AR, or Voltage=Current*Resistance

From that we get E/I=R, and I=E/R

That's Ohms Law, or a first lesson in DC electric theory without all the thory.

As previously mentioned, the meter should be connected to the accessory side of the ignition switch, since the meter itself is a (very small) load and will draw a tiny amount of current.

If the meter is connected to a power source that's always on, then it should read something as long as the battery is connected. If it reads less than 12V something is loading the circuit the VM is connected to.

If the voltmeter reads 8 volts in a 12 volt system, its possible the battery isn't charged, a load is causing a drop in voltage, or both.

Sorry if that was a rant, but, but, ok, no excuses.

[kbs71]

Yea, what he said

[neonlarry]

Did you get Painless to build you a special harness for a voltmeter? Stock type harness would be for an ampmeter. And if you hooked the stock ampmeter wire to a voltmeter it would read 12V all the time.

[airdale94]

Originally Posted by neonlarry

Did you get Painless to build you a special harness for a voltmeter? Stock type harness would be for an ampmeter. And if you hooked the stock ampmeter wire to a voltmeter it would read 12V all the time.

Nuff said, I guess.

[mvfd70]

My 97 Z71 has a volt meter and it shows zero with the key off. Turn the key on and it reads 12 volts. Start the engine and it reads 13 to 14 volts. I only mention this because I had a cell in my battery go bad the other day and with the key on and engine off it only read 8 to 10 volts. I know this isn't a 67-72 truck but it's the same principle. I agree with others saying that the volt meter should read 0 with the key off. I also agree with the above couple of statements that say that you have a volt meter hooked up to a wire that should be an ammeter. Change the volt meter to a switched power source and/or install an ammeter where you have the volt meter hooked up to now.

[gator2511]

Voltage does flow through a load. That how we get voltage drops in series circuits.

['70_402]

Originally Posted by neonlarry

Did you get Painless to build you a special harness for a voltmeter? Stock type harness would be for an ampmeter. And if you hooked the stock ampmeter wire to a voltmeter it would read 12V all the time.

you da man...... like i said to begin with, i couldn't remeber if it went to 0 when the key was off or not..... maybe i just had a battery going bad....