Wiring a voltmeter?

G'day.

I have been wanting to fit a voltmeter to my bay for ages. Today I acquired one. It's ford badged and came out of some sort of truck, but is designed for 12v systems.

I'm afraid the wiring has me a little confused.

It has three terminals.

GND which is part of the gauge case.
+ ... well thats power, and is of course insulated from the case.
? A third unmarked terminal which is also insulated.

I get about 12v from connecting + to the battery, and uh... resting the gauge on the motor. Just testing before install.
At first I tried + and the mystery terminal. It buried the gauge at the top.

Can I safely ignore the mystery terminal? It's not for some kind of reference voltage or anything is it?

The rest of the wiring I can handle not a prob. Actually considering putting in a switch to swap inputs between main and aux batteries.

While on this topic, where can I get the bulb and bezel that clips into the back of gauges?

most likely its just illumination terminal

u need to wire the gauge in to the ignition circuit, otherwise itll flatten the battery if its reading all the time

i think you will find a volt meter need both positive and negative direct to the battery to get the best reading

an AMP meter needs to be in line from memory

to the ignition circuit, otherwise itll flatten the battery if its reading all the time

yep only when the key turned on

Yeah, it'd be hooked up to the ignition feed. As it is the main reason I am fitting it is to figure out whether there is a charging issue.

The other post is not for backlight. The backlight is an external entity in the form of a globe and a clip in bezel, which I do not currently possess.

When gnd is earthed, and + is connected to the battery the voltage looks reasonable.
However I am not totally convinced, as I believe the voltmeter is wired similarly to the voltmeter style fuel gauge, if you know what I mean.

About all I can do it seems is connect it, and check the results against a multimeter, ignoring the mystery terminal.

I also intend to connect the auxiliary battery via a switch, so I can have main (via ignition), aux (just have to remember to flip the switch back) or off.

I apologise if I was not clear enough previously.

vw54 wrote:i think you will find a volt meter need both positive and negative direct to the battery to get the best reading

an AMP meter needs to be in line from memory

yes... easy way to remember it is that a voltmeter measures the volts ACROSS a part of the circuit... ie battery
amp meter measure the current flowing THROUGH a part of the circuit. so it has to be in series within the circuit