after got problem on my power windows switch........
every time I drive my car, when she goes around 25-40 Miles/hr....the Volts will drop to about 12.5V........probably in Local......but when come to highway....should be over 45m/hr, Volts back to 14.2v to 14.4v, it also comes back to over 14.2v when turn on the HID.
some of peopel tell me that is not problem but..........it never happened before......
so have any idea about that????
sorry about my poor English and thx for help.....

 

it's difficult to understand your question... but if you are asking if 12.5 V at idle is unusually low, then no. i generally see closer to 13.5-9 at RPM's above 2k.

 

no my car is 12.5v at 25-40 miles/hr, not about RPM
but when you turn on the light, then it's ok at 14.1-14.4v
turn off the light, it will drop to 12.5v, but not in the same time...about 5 sec

 

At idle with no accessories on, your battery voltage should be between 13.5 and 14.5V. As you start to turn on A/C, headlights, fan etc. the voltage will drop down, but raising the idle should bring it back up. If not, your alternator is not cranking out enough power. Could be bad brushes, bad diode, bad voltage regulator. Where are you measuring the voltage?

The output of the alternator is affected by engine RPM, not vehicle speed. Is your charging system indicator light on?

 

no I have volt gauge

 

You didn't answer my questions.

Where are you measuring the voltage?
Is your charging system indicator light on?

 

no indicator light on
and I just read the votage gauge

 

Sorry, I didn't know that you had a built-in voltmeter. I thought you were using a portable one.

If the charging light is not coming on, you are probably OK.

You bought this car used, right? Try to find out where the voltmeter is connected.

 

I bought this car used but in stock, all gauges I installed by myself........the voltmeter (-) connect to ground and (+) to the CD Player ignition ON.....