Volt Meter measures a difference in voltage AROUND an item in a circuit or the whole circuit. its a none invasive piece of instrumentation.
Ammeter has to be IN the circuit. its a device in the actual circuit and as such must have nearly no resistance so it doesn't disrupt functions of the other components by using the current itself, it also needs to be rated higher than max current flow in order not to melt.
a car ammeter is really a milliamp meter with a bus bar inside most of the current through it bypasses the meter part via a precisely controlled low resistance short circuit, the bus or buffer or Shunt, while the rest swings the needle hence if the gauge parts fails the car still runs
Voltmeter has near infinite resistance (in context) if it allowed current through it it would not measure accurate volts
Ammeter is in circuit it has a resistance that tends toward infinitely small (in context) if it didn't it would have a voltage across it and it would mess up its own measure of current
volt meter measures the push from the battery or alternator by comparing before and after a thing that makes use of electrical energy, in our case the whole system.
ammeter measures the flow caused by the PUSH in relation to the FIGHT against the flow (resistance/ impiedence/ inductance) that the components in the circuit put up
Converting the actual electromechanical meter is not worthwhile it can be done but you have a centre scale meter and it involves massive resistors and messing about to a great extent
see here
https://www.niser.ac.in/sps/sites/defau ... -versa.pdf
replacement is the good option
you need a vintage looking pod mounted meter of appropriate size and pointer colour, in my case a modern VDO would work as my car has vintage Aussie VDO gauges. and id be looking for a face that is mounted with 2 small screws at a specific metric spacing to avoid drilling my cluster face with a tiny drill....if you have to the excess holes will be covered by your new decal...but still
it will need to be de mounted from its pod and the guts mounted where the ammeter goes
before you do that it is worth scanning the front of the ammeter and the front of the volt meter and taking it to a vinyl place to get a gauge face transfer made.... thus you can get ammeter style font and background and they can copy the volt meter scale on
once its all mounted and you applied your decal
you join the wires that used to go to the ammeter together and bind them up nice in loom tape and stick em some where safe in the depth of the dash
you connect 1 lead, the negative of the volt meter, the black wire, to earth/chassis i.e to the pod or dash mounting screws
you connect the red lead to any, and i mean any ignition switched 12 volt feed. suggest the switched end of the fuse box.
that way your volt meter always measures the difference between - battery post connected to the chassis and the 12 volt feed coming from the splice under the dash (i.e supplied from battery or alternator or both)
the meter needs to be a 0-16 or 20 volt meter as it will spend most of its time at 14.3 Volts. but don't get a 0-50 volt any granularity in what you measure is lost with an inappropriate scale
if its needle jiggles, in a really annoying way and looks LOW QUALITY as it fights to track what your mechanical voltage regulator is doing
get a small inductor from an electrical supply shop you are looking for a small iron ring with a coil of wire around it
put it in the red wire it will act as a voltage damper smoothing the movement of the needle on the scale
basically any voltage spike has to create a magnetic field before it hits the gauge which smooths things considerably
some experimentation might be necessary with this and the inductor needs to be 12- 15 volt rated current rating can be tiny as volt meter sinks next to no current. it has a massive resistance so does next to nothing in relation to flattening your battery....
the bulb used to illuminate it will use 10 times more energy than the meter itself.
Dave
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