Volt meter power

[Learpilot]

I need some  Team Smart help. Thanks in advance !!!
The wife and I were crusin Sunday evening after dark, everything seemed A-OK until I looked down at the volt meter. It was showing 12 volts not the 13+ like it always has shown in the past. So after we got back home I got out my VOM and checked the Alternator output voltage, it was 14.5. I shut off the engine to read the battery voltage, it showed 12.7. The next morning I checked Battery voltage and it still showed 12.6. I still was not sure of the alternator was A-OK , so I took it down to the local Auto parts store and let them check it. It checked out A-OK.
That got me thinking (maybe a bad thing) if I had a wire coming from the alternator to the volt meter It would show the Alternator output voltage. The only problem with that is the volt meter would not shut off. I can use a relay to act as a switch then it will work. I have a Ez-wiring wiring harness and it uses the gauge power to power the volt meter. I think the reason the volt meter was showing 12 volts was because of the battery was full plus the volt meter was showing the draw from the headlights being on(I have the head lights on a relay).
Do any of you smart guys see a problem with doing this ?
Thanks , Rick Harris

[enjenjo]

I think you have a bad Voltmeter, or a problem in the wiring. In general, the system voltage should be the same anywhere in the system. If it's not, then you have resistance somewhere. If the voltmeter is good, and it's reading a lower voltage than at the alternator, then you have to fix something.

[wayne petty]

will you do a voltage drop test...

meter @ 20vdc scale...

engine running...

pos battery term to neg battery term... 14+ volts..

neg bat term to engine block   less than 0.02 volts

neg bat term to frame     less than 0.02 volts..

neg bat term to dashboard grounds.. less than 0.02 volts...

positive bat term to alternator output term.. less than 0.5 volts... engine running also...there is a lot more current running here..

pos batt term to the differnt fuses under the dash...     there are usually several circuts suppling power to them.. if any have resistance it will show up in this test....

since volt meters are looking at the differnce in voltage if there is resistance in the ground circut it will usually show up when doing this test....

i also usually do this with the headlights on and accessorys running..

and i do one more test...

neg bat term to engine block  while cranking the motor... this should read less than 1 volt while cranking...  if it reads more... put a set of jumper cables between the neg term and block and try again...

remember.. electrons flow from - to +  and no circut will work with only one side connected...

hope this helps.....


i am curious why your in car volt meter would be reading low...

[Learpilot]

will you do a voltage drop test...  

meter @ 20vdc scale...

engine running...  

pos battery term to neg battery term... 14+ volts..

neg bat term to engine block   less than 0.02 volts

neg bat term to frame     less than 0.02 volts..

neg bat term to dashboard grounds.. less than 0.02 volts...  

positive bat term to alternator output term.. less than 0.5 volts... engine running also...there is a lot more current running here..

pos batt term to the differnt fuses under the dash...     there are usually several circuts suppling power to them.. if any have resistance it will show up in this test....

since volt meters are looking at the differnce in voltage if there is resistance in the ground circut it will usually show up when doing this test....  

i also usually do this with the headlights on and accessorys running..  

and i do one more test...  

neg bat term to engine block  while cranking the motor... this should read less than 1 volt while cranking...  if it reads more... put a set of jumper cables between the neg term and block and try again...  

remember.. electrons flow from - to +  and no circut will work with only one side connected...

hope this helps.....


i am curious why your in car volt meter would be reading low...

I drove the car today and the volt meter shows more normal voltage. Maybe after taking off the alternator and putting it back on helped get rid of some corrosion. The alternator had no sign of corrosion, but it may have been there. The battery terminals are also clean. I am running a gel cell battery.
Thanks for all your help and I will do the test you suggested.
Thanks again, Rick Harris