Hello Everyone,
does anyone know how to convert an
ammeter to a voltmeter? I don't want it to go up in smoke! Any help would be appreciated!!!
Thanx

You mean with the same device? That won't work, the ammeter measures current flow and the volt meter measures well voltage.

I'm somewhat unsure if an ammeter is a good thing, for one, all of the current for the car has to go through the gauge.

If i were overengineering things, I'd use a current sensing transformer on the +12 at the battery and use that to drive a meter so as to not have all the current going to the gauge.

No, not to convert , but a different gauge alltogether ( hence the word,swap)sorry for any confusion, besides my own...

Autometer ammeter install instructions, scroll down a bit ( 1.7 MB pdf )

that diagram made minimal sense to me, apparently they can measure amperage without running the full current through the thingie.

It looks really easy.

You only need a small fraction of the current to pass through the guage to understand the total amount of current going through the system.

EDIT: Sorry didn't didn't read previous post!


But it is true. I havent read that link but if you stick a parallel circuit over a componant with some resistance (prefferable much higher than the componant) you will draw a small amount of current through that resister. The trick to understanding current is to imagine it like plumbing. Most of the current will go through the main componant with little comparitive resistance (ie large pipe) and a small amount will go through the higher resistance componant (ie small pipe).

If you have a 7K resistor and a 3K resistor in parallel, 70% percent of the current will pass through the 3K resistor and 30% will pass through the 7K resistor.

In the case of an ammeter it would be more like a 10K resistor and a 1000K(1M ??) resistor in your ammeter. So the amount of current passing through the ammeter will only be 1% of the total.

Sorry to all you electronics buffs for my crude interpretation and use of lingo!.

The actual amp gauge is a voltmeter. It measures the voltage across the shunt resistor when current is flowing through it. It's a small amount of voltage that's relative to the current. You do some ohm's law and write AMP on the dial and wa la... amp meter.
You have to hook the voltmeter up to an IGN +12V source or the gauge will always be on. I don't think ampmeters are hooked up this way so the wires for the ampmeter are not used.

its pretty hard to blow up an ammeter whe measuring voltage. When you measure voltage, you measure in parallel with the component your measuring accross. When you measure current, you measure in series. If you put your ammeter in series with your starter motor when you crank it over your going to blow it obviously because of the high amount of current.

on your ammeter you should have 2 plugs, one for fused, one for unfused. (one should be marked 10Amp or something) If you only measuring small stuff, you can pretty much ignore the 10A plug. When your trying to measure an unknown current amount, swithch to 10Amp first, if you don't get a reading, swap to the smaller one.

Something like that anyway... its been a while since i was instructed how to use one

You wouldnt get me putting direct positive and negative across a guage that is meant to measure current running through it.

To answer the original question.
Simply connect both of the ammeter wires together.
Run 12V ign to the positive side of the voltmeter and an earth to the negative side.

hey people, perhaps I should give more info...
this "swap" is for my '65 Fairlady Roadster, w\ ammeter in the dash. A somewhat common problem with old "toadsters" is the gauge will fuse together, with no broken or shorted wires, and F"ing smoke the whole system! the gauge itself is the weakest link, bye-bye. can I just join the 2 wires with a 30 to 60? amp fuse? I think that's safer than relying on the gauge... fuses are cheap! thanx all for your input

Thank you and again should it be with inline fuse?