Voltmeter Question...Gauge says one thing, but Battery says another!

[91StangGT5.0]

Ok I have an Aftermarket Voltmeter wired in my car. When I take a read from the battery itself with the car off it's 12.9v. With the car on the battery reads 14.5v but the Voltmeter reads 13ish volts. I turned on the A/C on full blast along with the Headlights, Fog Lights, and my radio on turned up and the Voltmeter reads near 10v, but the battery reads around 13.0-13.3v. I have my Voltmeter wired with the radio's ground and to the fuse box. I want to match the reading on the battery with the gauge.

I also have an Underdrive crank pulley. It's the only underdrive I have. I also have a Cobra Overdrive water pump pulley.

 

[beyondspexj]

voltage drop is usual with the amount of load you put on the alt. do you have the stock alternator or a 3g?

 

[393strokervert]

is this a digital gauge? if so, some of them have a tiny screw in the back of them to allow adjustment of the voltage readout. this adjustment allows you to take say a handheld meter, read what the battery is at & then adjust your cars meter to that number.

 

[91StangGT5.0]

No it's not a digital gauge. I have a 130a 3g alt. I'm about to install a 200a 3g

 

[393strokervert]

have you tried taking the gauge out of the car & connecting it straight to the battery to see if it matches your handheld meter? I'm thinking it's possible that the connection to the radio ground is not very good.

 

[91StangGT5.0]

voltage drop is usual with the amount of load you put on the alt. do you have the stock alternator or a 3g?

It's not an issue of me not knowing what acessories do to the alt, but rather an inaccurate voltmeter gauge reading......

 

[91StangGT5.0]

have you tried taking the gauge out of the car & connecting it straight to the battery to see if it matches your handheld meter? I'm thinking it's possible that the connection to the radio ground is not very good.

No I haven't yet. I will in a bit though and let you know how it goes. I figure it would read the right voltage.