Originally submitted by T:
Fitting a Voltmeter:
A Voltmeter requires only the thinnest two wires connected to it to work
because the current it draws is only thousandths of amps (called milliamps).
Because it only needs thin wires a Voltmeter can be easily connected without interfering
with the Electrical System.
Connect the Positive Wire to a point that comes live with the Ignition and the Negative Wire
Any illumination for the device should be wired into the Parking Lights.
Reading a Voltmeter:
Once a few simple facts are known, reading a Voltmeter is child's play.
A normally functioning car will show the Alternator's Regulated Output Voltage
(the Voltage stamped on the Alternator) any time the Engine is spinning above 1,000 RPM.
If the Engine is Idling, the 14 Volt output will only be present if the Engine is running
with the Headlights, Wipers and Hi-Fi turned OFF.
At night the Voltage will progressively drop when the car is Idling unless the Idle Speed
has been increased to compensate.
If the car has an increase in its Electrical Load the Idle speed may need to be increased to compensate.
After a Cold Start and with the Wipers, Headlights, Internal Fans and other loads present
the Voltmeter will likely read under 12 volts and stay there until the engine RPM increases above 1,000 rpm. Once the Battery has been recharged the Voltage will not fall so far.
A Voltmeter tells you if the required System Voltage is present or absent and gives you strong indications of an Alternator that is falling in output over a period of time, or has just dropped dead.
A Voltmeter as a Fan Belt Monitor:
Irregular fluctuations by the Voltmeter can be caused by a loose fanbelt.A continual drop in the Voltmeter's reading will indicate a broken Fan Belt minutes before the Temperature Gauge gets around to it.