electrical problem
 

my original voltmeter doesnt work in my mustang so i decided to put a new one in, i had been having problems with electrical stuff ever since i had the car, well when i put the meter in the needle just starting jumping...it wouldnt ever stay in a steady spot...did i hook it up wrong or what kind of problem could cause this?

Where did you hook it up to? Were you opening and closing the door, or turning on the radio, etc?

well first i hooked it up where my radio used to be and it read 12 volts without the key on...then it read 14 when i turned on the car...then i hooked it up to the wires that ran my gas gauge, oil pressure and temperature gauge and on all of those it wouldnt hold a steady pulse...where would the propper spot be to hook it up?

sorry i meant it read 12 volts with the key off

You want to attach it to a hot lead from the battery, and a good ground. Don't attach any other wires directly to that circuit, because if wired in series, it will include their direct load in it's measurement, whereas what you are trying to read is the total overall load.

Take care,
~Chris

on post / ignition switch?
 

Doesn't he need to hook up to the "on" post or "accessory" post of the ignition switch? That way the volt meter won't read at all untill the ignition switch is activated either in the acc. position or the on position.

Rev

If he wants to. I run mine off the battery. I don't want to have to rely on the ignition switch working to get a reading. Besides, wiring it through the accessory terminal won't give you an accurate reading of the battery, because other demands will be on when the switch is in that position. If you want to read true battery voltage, it needs to come from the battery itself.

Take care,
~Chris

Can you leave hooked up like this for long periods of time? How many amps(mili?) will this pull?

I guess it depends on how fancy your voltmeter is. :)

If it's just a regular old dial gauge, the amount of energy it takes to hold that needle in place is a lot less than it takes to preserve your radio stations. I've left my truck by itself without being started for a couple months at a time, and it still started fine on it's own. Of course, I've left my headlights on before to, and had to jump myself from my auxilary battery, but that's another story. :)

Take care,
~Chris

Same?
 

I think the hot lead at my ignition switch reads the same voltage as at the + battery terminal. Of course mine is a simple, old car with few electrical accessories. The truth is that I still use my old stock amp meter, LOL. I only use the hand held multi-meter voltage meter is if I'm trouble shooting a problem.

Rev

A voltmeter is added to the accessory bus. On '65-'67 Mustangs this is a screw in the center of the ignition switch. On '68 and later, I'd have to refer to schematic wiring for the model year.

It is not added to the IVR bus, which is the instrument regulator bus. This would cause a modern voltmeter to jump all around and never give a constant reading like you describe. The fuel guage and temperature guage are on the IVR bus on an early Mustang... you can't use this for your voltmeter.